Lava Cakes
Banana Fluffernutter Lava Cake
Moist banana cake layered with whipped peanut butter buttercream, fresh bananas, and silky marshmallow lava.
Recipe by Angela Heckler
Prep
1 hr
Bake
22–25 min
Total
About 3 hr, including cooling and assembly
Yield
One 8-inch three-layer cake
Peanut butter, marshmallow fluff, and banana already belong together, but putting them into a layer cake makes every part of the combination more dramatic. The cake brings the deep banana flavor, the buttercream adds salt and richness, and the marshmallow filling stays soft enough to spill gently into each slice.
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Read this first
The quick notes.
Flavor
Ripe banana, salty peanut butter, vanilla bean, and sweet marshmallow.
Texture
Moist banana cake, cloud-like buttercream, fresh bananas, and silky marshmallow lava.
Best moment
Cutting the first slice and watching the marshmallow filling settle between the layers.
Thinking out loud
The fluffernutter cake I wanted to eat
The cravings, questions, and running commentary behind this bake.
I always have about four tubs of Dandies marshmallow fluff in the pantry because peanut butter and fluff might be the best combination ever. Add banana and my eyes roll back. I could live on this trio. I put it over ice cream all the time because it is easy, instantly melty, and never disappoints.
This cake turns that obsession into something unforgettable: moist, fluffy banana cake layered with silky marshmallow lava, fresh banana slices, and whipped peanut butter buttercream. The salty peanut butter balances the sweet marshmallow perfectly, while the banana makes everything soft, warm, and familiar. If you love fluffernutter, this might become your favorite cake.
I highly recommend Dandies marshmallow fluff. It behaves like a dream in this lava cake and gives the filling the completely perfect glossy, silky texture I want.
Ingredient notes
Key ingredients
Very ripe bananas for the cake
Use deeply speckled, very soft bananas and mash them completely smooth. Super-ripe bananas give the cake concentrated flavor, moisture, and an even crumb.
Fresh bananas for the filling
Use firm-ripe fresh bananas for assembly. They should be sweet but still sturdy enough to slice neatly and stay in place inside the buttercream dam.
Dandies marshmallow fluff
I highly recommend Dandies. It is vegan, behaves beautifully when loosened with warm cream and melted butter, and gives the lava filling its glossy, silky texture.
Creamy peanut butter
When it comes to peanut butter, you will only see Jif in this house. If you are a Skippy person, that is okay too. Whichever one you choose, it must be a smooth, shelf-stable creamy peanut butter. I do not recommend natural peanut butter for this recipe because it can separate, soften the buttercream, and leave it without enough structure to hold the filling.
Cake flour and cornstarch
Together they keep the banana layers soft and fluffy enough to balance the rich filling and buttercream.
Brands I used for this recipe
Curious what I used? These are the exact products I reached for while developing this recipe.
Yogurt
Plain unsweetened yogurt
Plain unsweetened yogurt adds moisture, acidity, and body so the crumb bakes up tender without tasting tangy.
Milk
Milk
Milk affects how smoothly a batter, filling, or frosting comes together. Soy milk and Ripple tend to emulsify well because their protein and fat help create a creamy, cohesive finish.
Butter sticks
Butter sticks
Use butter sticks for buttercream and fillings that need to hold their shape.
Heavy cream
Heavy cream
Heavy cream affects silkiness, looseness, and how buttercream or filling sets after chilling.
Marshmallows
Marshmallows and mallow
Use Dandies for marshmallows and mallow.
Cake flour
Cake flour
I use King Arthur Unbleached Cake Flour for this recipe.
Vanilla bean paste
Vanilla bean paste
I use Rising Star Baking Supply Vanilla Bean Paste for this recipe.
Marshmallow
Marshmallow
I use Dandies for the marshmallow in this recipe.
Testing notes
Why this works
Use two stages of banana ripeness
The cake needs very ripe, deeply speckled bananas for flavor and moisture. The filling needs fresh, firm-ripe bananas so the slices stay distinct and do not make the layers slippery.
Keep the marshmallow lava at room temperature
Let the filling stand until it is completely cool and slightly thickened but still pourable. Warm filling can soften the buttercream dam; cold filling can become too thick to settle smoothly.
Build a tall, complete dam
Pipe an unbroken ring of peanut butter buttercream around each layer. Keep the marshmallow lava below halfway up the dam, then arrange the bananas in a single layer.
Stop adding cream when the buttercream is ready
Stream the cream in slowly and stop once the buttercream is light, silky, and sturdy enough to pipe. The full amount may not be necessary depending on the butter and peanut butter you use.
Step by step
How to make Banana Fluffernutter Lava Cake
Step 1
Bake the banana cake layers
Use deeply speckled bananas in the batter and mash them completely smooth. Divide the batter evenly among the pans, bake until the centers spring back, and cool every layer completely before assembly.
Step 2
Start with buttercream and a tall dam
Spread a very thin layer of peanut butter buttercream over the first cool cake layer, then pipe a tall, unbroken dam around the outside edge.
Step 3
Add the marshmallow lava
Pour the completely cool, still-fluid marshmallow filling inside the dam. Keep it below halfway up the buttercream so there is room for the fresh bananas and the next cake layer.
Step 4
Arrange fresh banana slices
Slice firm-ripe bananas immediately before assembly and arrange them in one flat layer over the marshmallow lava. Avoid heavy overlaps so the cake stays level.
Step 5
Frost, chill, and drizzle
Add the final cake layer, apply a thin crumb coat, and chill until stable. Finish with the remaining peanut butter buttercream and a light peanut butter and marshmallow drizzle.
Step 6
Slice after the cake is stable
Cut the chilled cake with a clean, sharp knife, then let each slice sit for 15-20 minutes before eating. The buttercream softens and the marshmallow filling becomes silky again.
From Instagram
Watch the reel
Watch the banana layers, peanut butter buttercream, fresh bananas, and marshmallow lava come together.
Open the reelSmall things that matter
Tips for the best cake
Mash the super-ripe bananas for the cake until completely smooth so the layers bake evenly.
Bring the milk, yogurt, and buttercream cream to room temperature before mixing.
Use fresh, firm-ripe bananas for the filling and slice them immediately before assembly.
Cool the cake layers and marshmallow lava completely before stacking.
Arrange the fresh banana slices in one flat layer rather than piling or overlapping them heavily.
Troubleshooting
If This Happens
If something looks off, start here. These are the most common trouble spots I watch for with this recipe and how I handle each one.
The marshmallow lava is softening the buttercream
The filling is probably still warm. Let it cool completely to room temperature before assembly, while keeping it fluid enough to pour inside the dam.
The marshmallow filling is leaking
Pipe a tall, unbroken buttercream dam and keep the filling below halfway up it. Chill the stacked cake before adding the final frosting coat.
The peanut butter buttercream is too soft
Stop adding cream as soon as the buttercream is silky and sturdy enough to pipe. Use smooth shelf-stable peanut butter, since natural peanut butter can separate and weaken the frosting.
The cake layers are sliding
Use firm-ripe bananas in one flat layer without heavy overlaps, and make sure the cake and filling are cool. Chill the assembled stack until stable before finishing the outside.
Before you slice
Texture and serving notes
For clean slices, chill the assembled cake until stable and use a sharp knife wiped between cuts.
Let each slice sit at room temperature for 15–20 minutes so the buttercream softens and the marshmallow lava becomes silky again.
Drizzle the finished cake with a little warmed peanut butter and reserved marshmallow lava, if desired.
Keep it good
Storage
Fridge
Keep the assembled cake covered in the refrigerator because it contains fresh banana and a cream-based filling.
Note 2
For the best fresh-banana texture, serve within 2 days. The cake remains safe for up to 3 days when properly refrigerated.
Note 3
The cake layers, marshmallow lava, and buttercream can be prepared one day ahead and stored separately. Add the fresh banana slices only during final assembly.
Recipe FAQ
Questions that come up
Can I make this banana fluffernutter cake dairy-free?
Yes. I recommend Dandies marshmallow fluff, Forager Unsweetened Plain Yogurt, Silk Original Unsweetened Soy Milk, Country Crock Plant Butter Sticks, and Country Crock Plant Cream or Silk Dairy-Free Heavy Whipping Cream. Keep the listed amounts and temperatures the same.
Why do I need different bananas for the cake and filling?
Super-ripe, deeply speckled bananas are best for baking because they give the cake concentrated flavor and moisture. For the filling, use the kind of fresh, newly ripened banana you would be happiest eating on its own. That clean, just-ripe banana flavor is exactly what you want between the layers.
Can I use natural peanut butter?
No. Use a smooth, shelf-stable creamy peanut butter for this recipe. Natural peanut butter can separate and make the buttercream too soft to support the marshmallow filling.
How do I keep the marshmallow filling from leaking?
Cool it completely to room temperature, pipe a tall and unbroken buttercream dam, and keep the filling below halfway up that dam. Chill the cake briefly after stacking before adding the final coat.
Can I assemble the cake ahead of time?
Yes, but because the filling includes fresh bananas, it is best assembled no more than one day ahead. Keep it covered and refrigerated, then let slices soften briefly before serving.
Should I weigh the ingredients or use volume measurements?
I strongly recommend weighing the ingredients in grams for the most reliable result. Volume measurements are included for convenience, but the amount in a cup can change depending on how an ingredient is filled, packed, or poured. These recipes are easy to follow, but their ratios are precise, so I cannot guarantee the exact same result when volume measurements are used. I still use teaspoons and tablespoons for small amounts like leaveners, salt, spices, and flavorings because those are the most practical measurements.
Can I make this recipe gluten-free?
I have not tested this recipe with gluten-free flour, so I cannot guarantee the same texture, rise, or structure. If you would like to experiment, a cup-for-cup (1:1) gluten-free baking blend intended to replace all-purpose flour is the best place to start. Results may differ from the recipe as written.
Can I use all-purpose flour instead of cake flour?
Yes, but the cake will have a slightly sturdier, less fine crumb. You can replace the cake flour with the same amount of all-purpose flour by weight. For a closer substitute, use 105 g all-purpose flour plus 15 g cornstarch for every 120 g cake flour called for, whisking or sifting them together well. If the recipe separately lists additional cornstarch, keep that amount in the recipe too; this mixture replaces only the cake flour.
More lava cakes to try
Measurement note
For the closest match to the recipe I tested, use grams. Volume measurements are included for convenience, but cups can vary, so I cannot guarantee the exact same result when measuring by volume.
Ingredients
Tap each ingredient as you use it.
Banana Cake Layers
- 305 g cake flour
- 10 g cornstarch
- 1 1/2 teaspoons baking powder
- 3/4 teaspoon baking soda
- 1 teaspoon fine sea salt
- 220 g light brown sugar, packed
- 120 g granulated sugar
- 150 g neutral oil
- 160 g plain unsweetened yogurt, room temperature
- 2 teaspoons vanilla bean paste
- 260 g very ripe bananas, mashed smooth (about 2 medium bananas)
- 120 g milk, room temperature
- 1 teaspoon apple cider vinegar
Marshmallow Lava Filling
- 400 g marshmallow fluff (I highly recommend Dandies)
- 160 g heavy cream, warm
- 20 g butter, melted
- 1/4 teaspoon fine sea salt
- 2 teaspoons vanilla bean paste
Whipped Peanut Butter Buttercream
- 226 g butter, slightly cool
- 140 g smooth, shelf-stable creamy peanut butter
- 420 g powdered sugar, sifted
- 1/4 teaspoon fine sea salt
- 1 teaspoon vanilla bean paste
- Up to 120 g heavy cream, room temperature
For Assembly
- 2–3 fresh, firm-ripe bananas, thinly sliced
- Smooth peanut butter, gently warmed, for drizzling (optional)
- Reserved marshmallow lava for drizzling (optional)
Pan used
I use Fat Daddio's 8-inch anodized aluminum round cake pans for this recipe.
Instructions
- 1Prepare the pans and oven. Preheat the oven to 350°F. Grease three 8-inch cake pans and line the bottoms with parchment paper.
- 2Mix the dry ingredients. In a medium bowl, whisk the cake flour, cornstarch, baking powder, baking soda, and salt until fully combined.
- 3Mix the wet ingredients. In a large bowl, whisk the brown sugar, granulated sugar, oil, yogurt, vanilla bean paste, very ripe mashed bananas, room-temperature milk, and apple cider vinegar until completely smooth and emulsified.
- 4Finish the batter. Add the dry ingredients to the wet ingredients and whisk gently just until combined and no dry streaks remain. Do not overmix.
- 5Divide and bake. Divide the batter evenly among the prepared pans. Bake for 22–25 minutes, until the centers spring back lightly and a tester comes out clean or with a few moist crumbs.
- 6Cool the layers. Let the cakes cool in their pans for 10 minutes, then turn them out onto wire racks and cool completely before assembly.
- 7Make the marshmallow lava. Whisk the marshmallow fluff, salt, and vanilla bean paste until smooth.
- 8Slowly stream the warm cream into the fluff while whisking continuously, until the filling is glossy and fluid. Whisk in the melted butter until completely incorporated.
- 9Cool the lava. Let the filling stand for 10–15 minutes, then continue cooling it completely to room temperature. It should be slightly thickened but still pourable before it touches the buttercream.
- 10Make the peanut butter buttercream. Beat the slightly cool butter on medium speed for 3 minutes, until pale and smooth. Add the peanut butter and mix until fully emulsified and fluffy.
- 11Add the powdered sugar, salt, and vanilla bean paste gradually on low speed. Increase to high and beat for about 7 minutes, scraping the bowl as needed, until very light.
- 12With the mixer on low, slowly stream in the room-temperature cream. Stop as soon as the buttercream is silky, fluffy, and sturdy enough to pipe a tall dam; you may not need the full amount.
- 13Prepare the fresh bananas. Slice the firm-ripe bananas immediately before assembly so they stay fresh and hold their shape.
- 14Build the first layer. Place one cooled cake layer on a cake board. Spread a very thin layer of peanut butter buttercream over the top, then pipe a tall, unbroken buttercream dam around the edge.
- 15Add the first filling. Pour in enough room-temperature marshmallow lava to stay below halfway up the buttercream dam. Arrange fresh banana slices over the lava in a single layer without heavily overlapping them.
- 16Repeat the filling. Add the second cake layer and repeat the thin buttercream base, tall dam, marshmallow lava, and fresh banana slices.
- 17Finish the cake. Add the final cake layer upside down for a flat top. Apply a thin crumb coat and chill for 20–25 minutes, until stable.
- 18Apply the final coat of peanut butter buttercream. Drizzle with gently warmed peanut butter and reserved marshmallow lava, if desired.
- 19Chill and serve. Refrigerate the finished cake until set. For the best texture, let individual slices sit at room temperature for 15–20 minutes before eating.
Meet the baker
Angela Heckler
Angela Heckler is the recipe developer, baker, and photographer behind Obsessed Cakes. Her Old-Fashioned Donut Loaf series is a growing collection of cake-donut-inspired loaves with soft, deeply moist crumbs, buttery streusel, and crackly glaze. Angela develops and tests every recipe in her Arizona kitchen. Follow Obsessed Cakes on Instagram, TikTok, and YouTube.
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