Preheat oven to 350F, grease three 6" round baking pans and dust with cocoa powder. Line bottoms with parchment.
Place all dry ingredients into the bowl of a stand mixer fitted with a paddle attachment. Stir to combine.
In a medium bowl whisk all wet ingredients (pour coffee in slowly, while whisking, as not to cook the eggs if very hot).
Add wet ingredients to dry and mix on medium for 2-3 mins. Batter will be very thin.
Pour evenly into prepared pans. I used a kitchen scale to ensure the batter is evenly distributed.
Bake until a cake tester comes out mostly clean. A total of 30-35mins.
Creme Egg Buttercream:
Beat butter until pale and smooth (2mins). Add in powdered sugar 1 cup at a time and beat until smooth (2-3mins). Add vanilla and heavy cream and beat until well combined (1-2mins). Add in chopped up creme eggs and beat on med-high to break chocolate into smaller chunks.
Spread on cooled cake.
Notes
*Note: The buttercream is very sweet. It goes well with the not-too-sweet chocolate cake, but if you don't like super-sweet frostings, I suggest cutting back on the sugar and/or Creme Eggs. Buttercream recipe adapted from Beyond Frosting.