Cake Layers
Whisk together flour, corn starch, baking powder, and salt.
Cream butter and sugar.
Add oil and vanilla. Mix.
Add eggs one at a time, mixing after each.
Add flour mixture and buttermilk alternately, mixing on low.
Bake at 350F for 30 minutes.
Cool layers completely.
Chocolate Buttercream Frosting
Melt ¼ cup butter. Mix with cocoa powder.
Melt ⅓ cup chocolate with ¼ cup milk.
Beat 1 cup room temperature butter.
Add melted butter-cocoa mixture. Mix.
Add powdered sugar and mix on low.
Pour in chocolate mixture. Add ¼ cup milk.
Mix until smooth.
Assemble Cake
Spread frosting on first layer. Add second layer. Repeat.
Cover cake with frosting. Swirl with spatula.
