I always start by bringing eggs and butter to room temperature. This ensures the batter mixes smoothly and the cake bakes evenly. Sifting dry ingredients together helps avoid lumps and gives a tender crumb.
Combine butter, sugar, and oil, then add eggs one at a time. Slowly fold in the dry ingredients alternately with buttermilk, vanilla, and vinegar. Stop mixing once everything is just combined to keep the cake soft.
Divide the batter evenly between prepared pans. Bake at 350°F (175°C) for 35–40 minutes or until a toothpick comes out clean. Let them cool completely on a wire rack before frosting.
Spread black cocoa buttercream between layers and around the cake. For a fun twist, I sometimes splatter white food coloring on top for a starry effect or add paper bats for Halloween.