For the chocolate cake layers: Preheat the oven to 350 degrees F. Line two 8-inch round cake pans with parchment, then spray with nonstick baking spray.
In the bowl of an electric mixer fitted with the whisk attachment, sift together the flour, sugar, cocoa, baking powder, baking soda and salt. Add the butter and coffee and mix on low speed until the butter "grabs" a lot of the dry ingredients--otherwise you will have a poof of cocoa powder and flour to contend with! Turn the speed up to medium and mix until well blended, about 1 1/2 minutes. Scrape down the sides of the bowl. Turn the mixer to low and add the eggs one at a time, mixing just until each one gets incorporated. Scrape down the bowl, add the vanilla and mix a little longer, 10 to 15 seconds.
Pour the batter into the prepared pans. Bake until a toothpick inserted in the centers comes out clean, about 40 minutes. Cool on racks for 10 to 15 minutes, then invert onto plastic wrap and wrap well. Place in the freezer for 8 hours or overnight. When ready to use, thaw at room temperature, still wrapped, for 1 hour before cutting.
For the caramel Irish cream buttercream: Place the egg whites and sugar in a metal bowl and set over simmering water. Whisk constantly until the sugar dissolves and the mixture is very thin and warm. Remove from the heat and pour the sugar mixture into the bowl of a stand mixer. Whip on high speed until stiff peaks form, about 5 minutes. Turn to low speed and continue to whip until the bowl is cool to the touch.
Turn the speed to medium and beat in the chunks of butter. (The mixture may appear curdled at first, but continue beating and it will come together.) Add the vanilla extract, then the liqueur and a little bit of the dulce de leche until it achieves a creamy texture.
(If your buttercream has sat for a while and lost its creamy texture, re-beat it before using.)
For the dark chocolate ganache: Place the chopped chocolate and cream in a medium microwave-safe bowl. Microwave on high power for 1 minute. Stir thoroughly with a fork or whisk, then microwave on 50-percent power for 1 minute; stir again. If there are some chunks in there, allow to sit for a few minutes, then re-stir. If necessary, continue with one or two more 15-second intervals at 50-percent power, being careful not to overheat the mixture. Add the vanilla if using.
Spray a piece of plastic wrap with nonstick spray, then cover the bowl, with the sprayed portion pressed directly against the surface of the ganache to prevent a skin from forming. Allow to sit until completely cool and set.
Assemble the cake: Use a serrated knife to cut the cake layers horizontally into 4 layers total. Smear a little buttercream on a serving plate, then top with a cake layer. Spread some ganache on the first layer, then spread some buttercream about 1/4-inch-thick on top of the ganache. Spread some buttercream on a second cake layer, then invert it to top the cake layer on the serving plate (buttercream will face buttercream). Repeat with the remaining layers of cake, topping each layer with ganache and then buttercream, and covering with a layer spread with buttercream, buttercream-side down. Once you have topped the cake with the last cake layer, use an offset spatula to smooth out any icing squishing out of the sides of the cake. Coat the entire cake with a thin layer of ganache for a "crumb coat." Place the cake in the refrigerator for about 20 minutes to firm up. Ice the cake with the remainder of the buttercream. Serve right away, or keep chilled. Allow the cake to come to room temperature before serving.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.