Prep Time 25 minutes mins
Cook Time 30 minutes mins
Resting Time 2 hours hrs
Total Time 2 hours hrs 55 minutes mins
Use room-temperature ingredients for a smoother batter and frosting, and adjust the red color based on your cocoa brand (natural cocoa gives a brighter hue than Dutch-process). If you don’t have buttermilk, make a quick substitute by mixing 1 cup milk with 1 tablespoon vinegar and resting 5 minutes. Coffee enhances chocolate notes without adding coffee flavor, but hot water works too. For cleaner slices, warm a serrated knife under hot water and wipe between cuts. The Oreo frosting thickens as the cookie crumbs hydrate, so aim for slightly softer than final texture when spreading, and if it becomes too thick, beat in 1 to 2 teaspoons milk. Store the cake covered in the fridge up to 3 days and let it sit at room temperature 20 to 30 minutes before serving for the creamiest texture.