Instructions Preheat the oven to 180ºC. Butter and flour 2 (9-inch) round cake pans, or lightly spray with baking spray, and line the bottoms with parchment paper.
In a large bowl, sift together the flour, baking soda, salt, and baking powder
In a large mixing bowl or the bowl of a stand mixer with the paddle attachment, add the butter. Beat on medium speed until creamy. In a medium bowl, whisk together the cocoa powder and oil. Add to the butter along with the sugars. Beat on medium speed until very light and fluffy, about 5 minutes, stopping to scrape down the bowl a few times during mixing.
With the mixer running, add the eggs, one at a time, beating well after each addition. Stop to scrape down the bowl as needed throughout mixing. Beat in vanilla.
With the mixer on low speed, add a third of the flour mixture followed by half of the milk and half of the sour cream. Continue alternating between the flour, milk, and sour cream until combined. Scrape down the bowl. Add the hot coffee and carefully whisk together until well combined. Pour the batter into the prepared cake pans.
Bake for 40 to 45 minutes or until the cakes are starting to pull away from the sides of the pans and the center springs back when gently pressed. Let the cakes cool completely in the pans. Carefully invert the cakes and remove the parchment paper. (The cakes are very tender and delicate so be gentle.)
Chocolate Buttercream Frosting ▢ 1½ cups unsalted butter room temperature (339g) ▢ ½ cup unsweetened cocoa powder (50g) ▢ ¾ teaspoon salt ▢ 1½ teaspoons vanilla extract ▢ 6 to 8 cups powdered sugar sifted (720-960g) ▢ 6 to 8 tablespoons heavy cream or whole milk (90-120ml)
In a large mixing bowl or the bowl of a stand mixer with the whisk attachment, whip the butter until very light and fluffy, about 5 minutes.
Add the cocoa powder, vanilla, and salt. Mix on low speed until well combined, stopping to scrape down the bowl a couple of times. With the mixer on low, gradually add in the confectioner’s sugar about a cup at a time alternating with a tablespoon of cream. (I like 6 cups of sugar for a smooth and swoopy frosting, but for a stiffer frosting, use up to 8 cups of sugar.) Scrape down the bowl.
Increase the speed to medium-low and beat until fluffy and spreadable, about 1 minute. Add additional cream a tablespoon at a time if your frosting feels too thick or stiff. This recipe makes enough frosting for 24 cupcakes or a 9-inch 2-layer cake.