Preheat oven to 325 degrees Fahrenheit. Line the bottom of two 8-inch cake pans with parchment paper, then grease pans and set aside.
Cream together sugar and butter and mix on high for 3-4 minutes, then scrape down sides. Add in your egg yolks, vanilla, and butter extract and beat until smooth.
In a large bowl mix together flour, baking powder, baking soda, and salt.
Add about ½ of your dry ingredients and ½ of your buttermilk to your creamed butter-sugar-yolk mixture. Mix until smooth. Repeat with remaining half of dry ingredients and buttermilk. Mix, make sure you scrape the bottom of the bowl with a rubber scraper to make sure everything has been mixed in.
In a clean bowl, with clean beaters. Beat your egg whites to stiff peaks. Take about ⅓ of your egg whites and gently fold them into your cake batter. Your batter should be uniform in color with no streaks. Then gently fold in your remaining egg whites until you have a uniform batter.
Divide your cake batter into 2 8-inch pans (can use 9-inch, just decrease bake time slightly). Bake at 325 for 30-35 until cake gently springs back when pushed on and a toothpick inserted comes out clean (a few moist crumbs is stuck to it are okay).
Chocolate Buttercream and Cake Assembly
Take your room temperature butter and beat for 1 minutes until light and fluffy. Then add in your cocoa powder, salt, vanilla, cream, and powdered sugar.
Start by beat on low (so your powdered sugar and cocoa powder don’t fly everywhere) and once the mixture comes together, turn the speed on high and beat for 3 minutes. Your frosting should be light and fluffy.
Once your cakes are completely cool, slice off the top of your cakes if they are domed so they are completely flat.
Spread a layer of frosting over your first cake layer and then stack your second layer on top. I like to place it top side down so you get a flatter top with less crumbs.
Then frost the top of the cake and outside edges of the cake. I used the back of a spoon to give my cake some “swoops” in the frosting. Slice and enjoy!
Notes
If you like a darker chocolate buttercream, use natural or dutch-processed cocoa powder.