White Chocolate Blondie Lava Cake

Ingredients

Volume measurements use US cups and level spoons and are approximate. Spoon flour and powdered sugar into the cup, level, then sift if directed. For cocoa and freeze-dried fruit powders, scoop the unsifted powder and level without packing, then sift if directed. Measure sprinkles loosely and level. Pack brown sugar. For ingredients marked "weigh for accuracy", use the listed grams.

Instructions

1. Make the vanilla cake layers. Preheat the oven to 350°F. Grease three 8-inch round cake pans and line the bottoms with parchment paper.
2. In a large bowl, whisk the granulated sugar, oil, plain unsweetened yogurt, milk, apple cider vinegar, and vanilla bean paste until fully smooth and emulsified.
3. Sift the cake flour, cornstarch, baking powder, baking soda, and salt directly over the wet ingredients. Whisk gently just until combined and smooth. Do not overmix.
4. Gently fold the rainbow sprinkles into the finished batter, stopping as soon as they are distributed. Divide the batter evenly among the prepared pans and tap them lightly to release large air bubbles. Add a few extra sprinkles to the pan tops if you like.
5. Bake for 22-26 minutes, until the tops are set and a tester comes out clean or with a few moist crumbs.
6. Cool the cakes in their pans for 10-15 minutes, then turn them out onto wire racks and cool completely before assembly.
7. Make the blondie batter lava. Melt the butter, granulated sugar, light brown sugar, and cream together over medium heat, stirring gently until the mixture comes together.
8. Remove the lava from the heat and stir in the salt and vanilla bean paste until glossy. Add a little more cream if you want a looser flow, then cool completely to room temperature.
9. Make the blondie cookie-dough pieces. Beat the room-temperature butter, light brown sugar, and granulated sugar until light and fluffy.
10. Mix in the prepared all-purpose flour, salt, and vanilla bean paste. Add the cream gradually until the dough is soft but scoopable.
11. Fold in the finely chopped white chocolate chips and rainbow sprinkles. Chill the dough briefly, then break it into pieces or cut it into small squares. Keep the pieces chilled until layering and garnish.
12. Make the vanilla bean buttercream. Beat the room-temperature butter on medium-high speed for 3-4 minutes, until pale and fluffy. Mix in the salt and vanilla bean paste.
13. Add the sifted powdered sugar in 3-4 additions, mixing until incorporated before adding the next portion.
14. With the mixer on low, slowly stream in 90 grams of the room-temperature cream. Add more cream only as needed to reach a smooth, pipeable consistency. The buttercream will firm slightly as it rests. For a sprinkle buttercream, fold in the optional rainbow sprinkles at the end; leave them out for the smooth finish shown in the photos.
15. Prepare to assemble. Make sure the cake layers and blondie lava are completely cool, the lava is fluid but not warm, and the cookie-dough pieces are chilled.
16. Place the first cake layer on a cake board. Spread a thin layer of buttercream over the cake, then pipe a tall, unbroken buttercream dam around the edge.
17. Spoon a controlled layer of blondie batter lava inside the dam, keeping it below the top edge. Scatter chilled cookie-dough pieces over the lava without overfilling the layer.
18. Add the second cake layer and repeat with the thin buttercream layer, dam, lava, and chilled cookie-dough pieces. Top with the final cake layer.
19. Apply a thin crumb coat and chill the stacked cake until firm. Finish with the remaining vanilla bean buttercream.
20. Decorate with additional blondie batter lava and chilled cookie-dough pieces, keeping the lava cool enough that it does not melt the buttercream.