S’mores Layer Cake

Preparation

1. Step 1

   Make the cake: Set a rack in the center of the oven and heat to 350 degrees. Generously butter two 9-inch baking pans and line the bottoms with parchment paper.

2. Step 2

   In the bowl of a stand mixer fitted with the paddle attachment, combine the granulated sugar, flour, cocoa powder, baking powder, baking soda and salt. Whisk until well combined and no lumps remain.

3. Step 3

   In a separate medium bowl, whisk the sour cream, melted butter, oil, eggs and vanilla. Add the sour cream mixture to the flour mixture. Mix on low until the dry ingredients are moistened, then turn the mixer to medium-high and mix for 2 minutes, scraping the bottom and sides of the bowl halfway through, until the batter is well blended. Add the coffee and gently fold in with a flexible spatula.

4. Step 4

   Divide the batter evenly between the prepared pans and tap them on the counter a few times to release any large air bubbles. Bake until puffed and a toothpick inserted into the center comes out clean, 35 to 40 minutes.

5. Step 5

   Set the pans on a wire rack and let the cakes cool for about 20 minutes. Run a thin knife around the edges of each pan and carefully turn the cakes out onto the rack to cool completely. (You may have to tap the pans gently on the rack to release each cake.) Peel off and discard the parchment.

6. Step 6

   While the cakes cool, make the graham crumbles: Line a sheet pan with parchment paper. Combine the graham cracker crumbs, sugar and salt in a medium bowl. Add the melted butter and vanilla and mix until evenly combined. Use your hands to grab handfuls of the mixture, squeeze it together firmly, then place on the baking sheet. Repeat until all of the crumbs have been scrunched together and placed on the baking sheet. Use your fingers to break up the larger bits into smaller crumbles, about the size of a blueberry. (There will also be some loose crumbs on the pan.) Bake the crumbles until golden, fragrant, and crisp, about 10 minutes. Cool completely on the pan, then break up any larger crumbles if needed.

7. Step 7

   Make the buttercream: In the metal bowl of a stand mixer, whisk together the egg whites and sugar. Set the bowl over a medium pot of simmering water. The level of the water should be just below the bowl. Whisk frequently until the sugar has dissolved and the mixture is hot to the touch (160 degrees on a thermometer), 3 to 5 minutes.

8. Step 8

   Return the bowl to the stand mixer and use the whisk attachment to beat the egg-white mixture until stiff glossy peaks form, about 5 minutes. Remove the bowl from the mixer and tip the bowl on its side. (This will help with air circulation so your torch doesn’t extinguish.) Carefully use a kitchen torch to toast the top of the meringue until it is deep golden brown. Vigorously stir the torched meringue into the bowl. Repeat this process two more times. The meringue and bowl should be relatively cool by this point; if not, keep mixing on low until the mixture is at room temperature.

9. Step 9

   Switch to the paddle attachment and reduce the speed to medium-low. With the mixer running, add the butter, a few tablespoons at time, mixing until the butter has been incorporated before adding more. Mix until the buttercream is smooth and fluffy. If the mixture splits at any point, turn the speed of the mixer up for a few seconds and it will come back together. After all of the butter has been incorporated, beat in the vanilla and salt. The buttercream will be a creamy color speckled with toasted meringue bits. (If needed, chill the buttercream for up to 30 minutes to firm it up before frosting.)

10. Step 10

    To assemble: Trim the tops of the cakes flat if needed. Stir the buttercream vigorously to knock out any large air bubbles. Place one of the cakes, top-side up, on a serving platter and spread about 1½ cups of the buttercream over the top. Sprinkle with graham crumbles until completely coated, then press them gently into the frosting. Add a small dollop of frosting to the middle of the cake (this will help keep the two layers together) and top with the second layer of cake, top-side down. Spread a thin layer of buttercream all over the cake, leaving about 1 ½ cups buttercream in the bowl, and refrigerate the cake until the buttercream layer is firm, about 20 minutes.

11. Step 11

    Frost the cake with the remaining buttercream, then top with some of the remaining graham cracker crumbles (you will have extra; see Tip). Serve immediately, or keep the cake covered at room temperature for up to 2 days. (The crumbles will soften as they sit.) To serve, use a hot, clean and dry knife for the tidiest slices.