Preheat the oven and prepare your baking pans according to the instructions on the Devil's Food cake mix box.

In a large mixing bowl, combine the dry cake mix with the oil and eggs required by the package instructions.

Crucially, discard the water measurement called for on the box. Instead, hydrate the batter by pouring in the ¾ cup of carbonated citrus soda and ¼ cup of dark brewed coffee. (The carbonation forces microscopic air pockets into the batter for a towering lift, while the coffee deepens the cocoa notes).

Stir in the 2 tablespoons of black walnut flavoring. Mix the batter thoroughly until smooth and unified.

Bake according to the package directions. Remove from the oven and allow the cakes to cool completely on wire racks before frosting.

While the cakes cool, build the frosting. Place the 6 cups of confectioners’ sugar, ¾ cup cocoa powder, and ¼ teaspoon kosher salt into the bowl of an electric stand mixer. Pulse briefly to combine the dry ingredients.

Add the melted butter, ½ cup of brewed coffee, 2 tablespoons of black walnut flavoring, and ⅓ cup of milk or cream directly into the bowl.

Beat on medium-high speed until the ingredients bind into a thick, highly glossy, fudgy emulsion. Scrape down the sides of the bowl as needed.

Assess the texture of the frosting: if it is too loose and weeping, beat in an additional spoonful of confectioners' sugar. If it is too dense and tears the cake crumb, stream in a tiny splash of milk until perfectly spreadable.

Generously frost the cooled layers, swirling the thick icing heavily over the top and sides of the cake. Serve immediately.