Ingredients
For the cake:
- 2 cups all-purpose flour
- ½ cup black cocoa powder
- ⅓ cup natural unsweetened cocoa powder (not dutch processed) See FAQs in blog post for answers to ingredient questions.
- 1 ⅔ cups sugar
- 1 teaspoon baking soda
- ½ teaspoon baking powder
- ½ teaspoon salt
- 1 ½ cups buttermilk
- ⅓ cup vegetable oil
- ½ cup unsalted butter, softened (not warm or hot butter, just set the butter out a couple hours beforehand so that it will be soft enough to mix well)
- 1 teaspoon white vinegar
- 2 teaspoons vanilla extract
- 3 large eggs
For the frosting:
- 2 cups unsalted butter, room temperature
- 1 pinch of salt
- 2 teaspoons vanilla bean paste (or extract)
- ¾ cup black cocoa powder
- ¼ cup natural cocoa powder
- 5 cups confectioner’s sugar
- 3 tablespoons milk (can add in another tablespoon if needed)
Instructions
For the cake:
- Set out the buttermilk and eggs ahead of time so they can come closer to room temperature before mixing the batter. (This is important.)
- Preheat oven to 350 degrees F. Grease and flour two 8-inch round cake pans.
- In a large mixing bowl, add the flour, both cocoa powders, sugar, baking soda, baking powder and salt. Mix well with a whisk and set aside.
- In another bowl, add the buttermilk, oil, softened butter, vinegar, vanilla and eggs. Whisk well.
- Add the liquid ingredients to the dry ingredients and mix on medium speed only until the ingredients are just combined. Scrape down the sides of the bowl and mix again until well combined. Be careful not to mix too long or the cake will turn out dense. Stop mixing once the ingredients are well combined.
- Pour the batter into the prepared pans and bake for approximately 35-40 minutes. The cake is done when a toothpick inserted into the middle of each layer comes out with a few moist crumbs on it or clean, but no raw cake batter on it.
- Set on wire racks to cool for about ten minutes, then turn out the cake layers onto the racks and remove the pans to cool completely before assembling the cake and adding buttercream frosting.
For the frosting:
- Add the butter, salt and vanilla to a large mixing bowl. Mix with an electric mixture on medium speed until smooth..
- Add both cocoa powders and mix on low until combined, then on medium until well incorporated. Scrape down the sides of the bowl and mix again.
- Add in 3 cups of confectioner's sugar. Mix on low until combined, then on medium until fully incorporated.
- Add 2 tablespoons of milk plus the last 2 cups of confectioner's sugar. Mix on low until combined, then on medium until fully incorporated. Scrape down the sides of the bowl, then mix again.
- Check the texture of your buttercream and if it’s still too thick, add milk only a tablespoon at a time, and mix after each addition.
- If you want the buttercream to be a deeper black you can add in a bit of black gel food coloring, but it is not generally necesseary as the black cocoa powder is fairly dark on it's own and seems to darken the longer it's on the cake.