Peanut Butter S’mores Cake

Ingredients

For the Chocolate Buttermilk Cake:
• 1 cup plus 2 tablespoons (140 grams) all-purpose flour
• 1 cup (200 grams) granulated sugar
• 1/4 cup (30 grams) plus 1 tablespoon unsweetened Dutch-process cocoa powder
• 1/2 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/4 teaspoon regular salt
• 1/3 cup (80 ml) plus 1 tablespoon buttermilk
• 1 stick (1/2 cup, 113 grams) unsalted butter, melted
• 1 large egg
• 1 large egg yolk
• 1 teaspoon pure vanilla extract
• 1/3 cup (80 ml) boiling water
For the Peanut Butter Swiss Buttercream:
• 3 large egg whites (85 grams)
• 1 cup (200 grams) granulated sugar
• 1 cup plus 4 tablespoons (283 grams) unsalted butter, softened
• 1 teaspoon vanilla extract
• 3/4 cup (170 grams) peanut butter
For the Chocolate Drizzle:
• 1 1/2 ounces (42 grams) bittersweet chocolate, chopped
• 1/4 cup (60 ml) heavy cream
• 1 tablespoon light corn syrup
For the Toasted Marshmallow Topping:
• 1 egg white (28 grams)
• 1/4 cup (50 g) granulated sugar
• 1 teaspoon light corn syrup
• 1/8 teaspoon cream of tartar
• 1 teaspoon pure vanilla extract
• some crushed graham cracker crumbs for topping

Instructions

For the Chocolate Buttermilk Cake:
1. Preheat the oven to 350 degrees fahrenheit and grease and line 2 6-inch baking pans.
2. In a large bowl (or the bowl of a stand mixer) mix together the flour, sugar, cocoa powder, baking powder, baking soda, and salt on low speed.
3. In a separate bowl, mix together the buttermilk, melted butter, egg, egg yolk, and vanilla extract until blended.
4. Add the buttermilk mixture to the flour mixture in 2 additions and beat on low speed until blended. Turn the mixer up to medium high and beat until smooth.
5. With the mixer on low speed, slowly pour in the boiling water and beat until blended. The batter will be thin.
6. Divide the batter equally between the cake pans and bake until a toothpick inserted into the center comes out clean, about 23-26 minutes.
7. Cool the cakes in the pans on wire racks for 15 minutes.
8. Turn the cakes out onto wire racks to cool completely.
For the Peanut Butter Swiss Buttercream:
9. Wipe down the bowl of a stand mixer with vinegar.
10. Add the egg whites and sugar to the bowl and place over a pan of barely simmering water. The bowl should not touch the water.
11. Remove the bowl from the heat, and whip the egg whites on medium high using the whisk attachment of your stand mixer.
12. Whip the egg whites until they become fluffy and double in volume. The bowl should be cool to the touch (this will usually take several minutes).
13. Turn the mixer down to medium low, and add the butter in one chunk at a time, until it has all been incorporated.
14. If the mixture looks curdled at this point, this is normal. Just keep whipping for a few more minutes until it comes together. If the mixture looks soupy, you can add a few cubes of chilled butter, or stick the whole bowl in the refrigerator for about 15 minutes and then continue beating.
15. Once the buttercream has become smooth, and the vanilla extract and peanut butter and beat until incorporated.
For the Chocolate Drizzle:
16. Add the chopped chocolate to a heat proof bowl.
17. Heat the heavy cream in a small saucepan until it barely comes to a simmer.
18. Pour 3 tablespoons over the chocolate and let stand for a few minutes so that the chocolate can melt.
19. Add the corn syrup and whisk until smooth.
20. If the mixture is too thick, add the remaining cream and whisk until you reach the right consistency.
For the Marshmallow Topping:
21. Wipe down the bowl of a stand mixer with vinegar.
22. Put the egg white, sugar, corn syrup, and cream of tartar in the bowl and place it over a pan of simmering water. (The water should not touch the bowl).
23. Whisk the mixture over the heat constantly until it reaches 130 degrees fahrenheit.
24. Transfer the bowl to the mixer and beat with the whisk attachment until thick and glossy and the mixture comes back to room temperature. It should hold stiff peaks.
25. Add the vanilla and beat to combine.
To Assemble the Cake:
26. Place one layer of the cake on a 6-inch cake board.
27. With an offset spatula, spread about 1 cup of the PB swiss buttercream filling on top of the first layer.
28. Place the 2nd layer on top.
29. Place the cake on a turntable, and apply a thin layer of the frosting on the sides and the top of the cake to lock in the crumbs.
30. Let the frosting set up in the refrigerator for about 15-20 minutes.
31. Apply the remainder of the frosting to the sides and top of the cake.
32. You can refrigerate the cake while preparing the chocolate drizzle and marshmallow topping.
33. Gently pour the chocolate glaze over the top of the cake until it drips down over the sides.
34. Sprinkle some graham cracker crumbs on top and gently press some onto the sides of the cake as well.
35. Put the marshmallow topping in a piping bag fitted with a round tip and pipe it over the top of the cake.
36. Using a kitchen torch, torch the topping until lightly browned.