This is an incredible classic birthday cake with a decadent chocolate cake slathered in a vanilla swiss meringue buttercream for the best of both worlds!
Pre-heat the oven to 350. Line two 9 inch cake pans with parchment paper and spray them both well with cooking spray. Then set up a stand mixer with the paddle attachment and combine the flour, two sugars, cocoa powder, baking powder, baking soda, cinnamon and salt in its bowl. Mix them together with the paddle just to aerate them, then slowly pour in the milk and oil, followed by the eggs and chocolate liqueur. Finally, very slowly and carefully pour in the boiling water with the mixer on low. Evenly divide the batter among the two prepared pans, then bake them for 30-35 minutes. A toothpick inserted in the center should come out completely clean. Let them cool in the pans for 15 minutes or so, then turn them out of the pans to cool completely. Clean out the stand mixer bowl and paddle since you will need them for the buttercream.
While the cake layers cool, make that aforementioned buttercream. Fill a small saucepan halfway with water and bring it to a low boil. Combine the egg whites, sugar and salt in a heat proof bowl and set it over the simmering water while you whisk it. Keep whisking while it gently cooks for a couple of minutes. Then transfer it into the stand mixer bowl and use the whisk attachment to whip it up to be stiff peaks for a few minutes. It should be white and shiny. Then switch to the paddle attachment and slowly add in the butter a stick at a time, finishing with the half stick. Finally, mix in the vanilla to finish it up! It will be a luscious buttercream. Then place the first layer on a cake plate and spead a thick layer of the frosting on it. Place the second layer on top and generously frost the top and sides of the cake. Decorate it to your hearts desire with edible beads, sprinkles, you name it! Enjoy!!