Lava Cakes
S’mores Lava Cake with Marshmallow Filling
Dark chocolate cake filled with gooey marshmallow lava and salty Golden Oreo crunch, finished with light chocolate buttercream.
This S’mores Lava Cake is built to taste like the whole campfire bite, not simply chocolate cake with a few marshmallows on top. Deep chocolate layers surround fluid vanilla-marshmallow filling, buttery Golden Oreo crunch, and a light, milky chocolate buttercream.
Cool every component completely, keep the marshmallow filling at room temperature, and build a tall buttercream dam before adding the lava. The finished cake is intentionally messy and generous, but those details keep the layers controlled until the first slice.
Recipe by Angela Heckler
Prep
1 hr
Bake
22-25 min
Total
About 4 hr, including cooling and assembly
Yield
One 3-layer 8-inch cake
Thinking out loud
It Had to Taste Like the Whole S’more
The cravings, questions, and running commentary behind this bake.
As a kid, if a bakery or dessert place offered a s’mores version of anything, I almost always chose it. I also remember thinking that a lot of those desserts did not quite taste like the s’more I had imagined. The cracker could disappear beneath the chocolate, and the marshmallow sometimes felt more decorative than soft and gooey. I walked into this cake with all of those memories and one rule: do not call something s’mores if it is really chocolate cake with a few s’mores notes here and there.
Naturally, it needed to be one of my lava cakes. My lava cakes are messy, a little unhinged, and designed as an overload for whoever is obsessed with that particular combination. The marshmallow fluff needed to coat every bite - not sit politely in one thin layer or show up only as a garnish.
The bigger question was how to keep the cracker element from getting buried. I could have spent more time thinking about it, but Golden Oreos came to mind and I could not get them out of my head. Cooked with butter, brown sugar, granulated sugar, and salt, they become crisp golden clusters that are familiar like a graham cracker but sturdy enough to hold their own between the soft chocolate cake and marshmallow lava.
The buttercream needed the same balance. It had to be milky, light, and chocolatey without becoming the only thing you tasted. Dutch-process cocoa gives it smooth depth, while natural cocoa keeps the chocolate brighter. I love things over the top, but every component still has to complement the others.
That is how this one was born: dark chocolate cake, marshmallow lava that reaches every forkful, salty golden crunch, and a soft chocolate buttercream holding the chaos together. It is absolutely excessive, but it still tastes unmistakably like a s’more.
Read this first
The quick notes.
Flavor
Dark chocolate, vanilla marshmallow, buttery golden cookie, brown sugar, and sea salt.
Texture
Moist cake, fluid marshmallow lava, crisp cookie clusters, and light chocolate buttercream.
Best moment
Pulling the first slice and watching the marshmallow settle around the crunchy golden layers.
From this recipe
Tested notes
Use the marshmallow lava at room temperature and keep it below halfway up a tall buttercream dam.
Reserve a little Golden Oreo crunch for decorating and serving.
Ingredient notes
Key ingredients
Dutch-process and natural cocoa powders
Using both gives the cake and buttercream a broader chocolate flavor. Dutch-process cocoa brings dark, smooth depth, while natural cocoa keeps the chocolate brighter so it does not flatten the marshmallow and cookie layers.
Hot brewed coffee and espresso powder
Coffee deepens the cocoa without making the cake taste like coffee. Adding it hot also helps the cocoa bloom so the chocolate flavor feels fuller.
Golden Oreos
Golden Oreos create a buttery, graham-like crunch that stays noticeable between the dark cake and soft filling. Include the cookie filling; it becomes part of the crisp, caramelized clusters.
Marshmallow fluff
Fluff gives the filling its unmistakable marshmallow flavor and stretchy body. Warm cream loosens it into a glossy lava that coats each bite while remaining thick enough to sit inside a buttercream dam.
Heavy cream
Warm cream smooths the marshmallow filling, while cream slightly above room temperature helps the chocolate buttercream become light and silky without cooling the butter too quickly.
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.
Dutch cocoa
Dutch-process cocoa powder
For Dutch-process cocoa, I typically reach for Majestic or Ghirardelli.
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Natural cocoa
Natural cocoa powder
For natural cocoa, I typically reach for Ghirardelli or Valrhona.
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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
Why two cocoa powders are used
Dutch-process cocoa makes the chocolate deep and rounded; natural cocoa adds a brighter chocolate edge. Together they keep the cake and buttercream rich without letting chocolate overwhelm the marshmallow and golden crunch.
Why the Golden Oreo crunch is cooked
Cooking the crumbs with butter, both sugars, and salt removes the greasy feel and toasts them into distinct clusters. Cooling the mixture in a thin layer preserves the crunch before it goes into the cake.
How to judge the marshmallow lava
The filling should be glossy and fluid enough to pour in a slow ribbon, but not watery. Let it cool completely to room temperature before assembly so it does not soften the buttercream dam.
Why the buttercream dam matters
The marshmallow filling is deliberately fluid. Pipe a tall, continuous ring and spread only a thin layer of buttercream beneath it. Keep the lava below halfway up the dam so the next cake layer rests on buttercream rather than floating on filling.
Why every component must be cool
Warm cake softens the buttercream, and hot cookie crunch or marshmallow filling can melt the dam. Cool the cake layers and crunch completely, and use the marshmallow lava only after it returns to room temperature.
Why the final chill is brief
A short chill steadies the buttercream and stacked layers without turning the marshmallow center firm. The goal is controlled lava, not a rigid filling.
How it comes together
From Instagram
Watch the reel
Watch the chocolate layers, Golden Oreo crunch, marshmallow lava, and toasted finish come together.
Open the reelSmall things that matter
Tips for the best cake
Sift the cake flour and cocoa powders so the batter mixes smoothly without prolonged whisking.
Divide the batter by weight so all three layers bake to the same height and stack evenly.
Spread the cooked Golden Oreo crunch in a thin layer and let it cool completely before breaking it into clusters.
Add the warm cream to the marshmallow fluff slowly while whisking so the filling stays glossy and cohesive.
Pipe a tall, unbroken buttercream dam and keep both the lava and crunch inside it.
Chill the assembled cake only until the buttercream feels steady, then let it soften slightly before slicing for the best lava texture.
Before you slice
Texture and serving notes
For the fullest lava effect, serve the cake cool rather than refrigerator-cold.
Use a long, sharp knife and expect a generous, messy slice; the marshmallow filling is designed to move.
Let refrigerated slices sit at room temperature until the buttercream softens and the marshmallow becomes fluid again.
Keep it good
Storage
Fridge
Store the assembled cake covered in the refrigerator for up to 4 days.
Counter
Refrigerate the marshmallow filling separately for up to 3 days, then bring it fully to room temperature and whisk until smooth before assembly.
Counter
Store the cooled Golden Oreo crunch airtight at room temperature for up to 3 days so it stays crisp.
Recipe FAQ
Questions that come up
Does this S’mores Lava Cake taste strongly like coffee?
No. The brewed coffee and espresso powder deepen the cocoa flavor, but the finished cake should taste like dark chocolate rather than coffee.
What if I can’t have coffee?
Replace the brewed coffee with the same amount of hot water and omit the espresso powder. The hot water will still help bloom the cocoa, although the chocolate flavor may be slightly less deep.
Why use Golden Oreos instead of graham crackers?
Golden Oreos create buttery, salted clusters that are sturdy enough to remain noticeable beside the soft cake and marshmallow lava. Their flavor still gives the cake that familiar golden-cookie part of a s’more without disappearing under the chocolate.
Can I use graham crackers instead of Golden Oreos?
I developed and balanced this cake with Golden Oreos, so they are my recommendation. Graham crackers contain less filling and may toast, absorb butter, and soften differently. You can experiment, but the crunch and sweetness will not be identical.
How do I keep the marshmallow filling from leaking out?
Cool every component, use the filling at room temperature, and pipe a tall, continuous buttercream dam. Keep the marshmallow below halfway up that dam and chill the stacked cake briefly before the final coat of buttercream.
Can I make the S’mores Lava Cake ahead?
Yes. Bake and wrap the cooled cake layers up to 2 days ahead. Make the crunch up to 3 days ahead and keep it airtight at room temperature. The marshmallow filling can be refrigerated for up to 3 days, but it must return fully to room temperature and be whisked smooth before assembly.
Can I use dairy ingredients?
Yes. I test with nondairy milk, yogurt, butter, and heavy cream, but their dairy equivalents can be used in the same amounts and at the same temperatures.
Can I toast the marshmallows on top without a kitchen torch?
Yes. Toast them separately under a closely watched broiler, then place them on the finished cake once they are cool enough to handle. Do not put the fully frosted cake under the broiler.
Why don't you provide volume measurements?
I know cups feel familiar, but weight is the most reliable way to give you the same result I tested. Flour, sugar, yogurt, milk, and other primary ingredients can vary a surprising amount when scooped or poured, while grams keep the recipe's ratios accurate. A scale is also faster and means fewer dishes because many ingredients can be weighed directly into the bowls already used in the recipe instead of requiring a full set of measuring cups. I still use teaspoons and tablespoons for small quantities like leaveners, salt, spices, and flavorings, where they are the most practical choice.
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.
Meet the baker
Angela Heckler
Angela Heckler is the recipe developer, baker, and photographer behind Obsessed Cakes. She is the creator of the Old-Fashioned Donut Loaf series, 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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