Make the Chocolate Pudding/Frosting:

1. In a medium saucepan, whisk together the cocoa powder, water, milk, and ¼ cup sugar. Place over medium-high heat and bring to a simmer.
2. Meanwhile, whisk together the egg yolks and the remaining ½ cup of sugar in a separate mixing bowl. Just before the milk mixture simmers, stir the cornstarch into the egg mixture.
3. Temper the simmering milk into the egg mixture by slowly whisking in a little bit of the hot milk at a time. Return the egg-milk mixture back to the saucepan and heat over medium-low.
4. Cook the pudding mixture, while slowly stirring, until it thickens and large bubbles pop at the surface. Add the chopped chocolate and butter. Whisk until completely smooth.
5. Strain the pudding with a mesh sieve into a clean bowl. Stir in the vanilla and the salt. Press a piece of plastic wrap directly onto the surface of the pudding and chill in the refrigerator until completely cool and thick, about 4 hours or overnight.

Make the Devil’s Food Cake:

1. Pre-heat the oven to 350°F. Grease and line the bottoms of three 8-inch cake pans with parchment paper and set aside.
2. Place the chopped chocolate and espresso powder in a large coffee mug or heat-safe bowl. Pour the boiling water over the top and whisk to combine. Place one of the cake pans on top of the mug to keep the contents hot and set aside.
3. Sift the flour, cocoa powders, baking soda, baking powder, and salt together and set aside.
4. In the bowl on a stand mixer fitted with a paddle attachment, add the butter and mix on medium until smooth. Add in the brown and white sugars and mix until light and fluffy, 2 to 3 minutes. Turn the mixer to low and add in the eggs and yolks, one at a time. Stop the mixer and scrape down the bottom of the bowl.
5. With the mixer on low, slowly add in half of the flour mixture and mix until combined. Stream in the milk and mix until absorbed. Add in the remaining flour and mix until combined. Stream in the melted chocolate mixture and mix until smooth.
6. Evenly divide the batter into the prepared pans and bake for 22 to 25 minutes or until a toothpick inserted into the center of the cakes comes out clean. Cool cakes on a wire rack for 15 to 20 minutes before removing the cakes from their pans.
7. Once the cakes have completely cooled, use a long serrated knife to cut the tops off of the cakes. Be generous here, but do not eat the scraps! We need them.

Assemble the Cake:

1. Remove the pudding from the fridge and gently whisk to loosen. Place one layer of cake on a cake board or serving dish. Spread on about 1/3 of the chocolate pudding with an offset spatula. Top with the next layer of cake and repeat. Place the last layer of cake on top (cut-side down). Chill the cake for about 10 minutes to set.
2. Once chilled, use the remaining pudding to frost the cake in a thin layer. Return the cake to the fridge for an additional 5 to 10 to slightly set.
3. Meanwhile, crumble the cake tops. You may use a food processor, a box grater, or just your hands. The cake crumbs should be fairly fine.
4. Remove the cake from the fridge and press the cake crumbs to the sides and top of the cake. This can get a bit messy, so work over a rimmed baking sheet for easier clean up. Reuse any cake crumbs that fall back onto the sheet pan and press onto the cake.
5. Store the cake in a cake box to prevent drying before ready to serve.

Decorate the Cake (optional):

1. Whip up a small batch of buttercream by mixing the butter and sugar until combined. Add the milk and vanilla, then mix on medium-high until light and creamy. Tint the buttercream your color of choice and mix to combine.
2. Place the buttercream in a piping bag fitted with a star tip. Holding the piping bag straight down, pipe stars around the top of the cake. Place dragees or sugar pearls on the tops of the stars.