Black velvet cake:

1. Preheat your oven to 350F. Grease 3 (6") round cake pans and line the bottoms with parchment paper. Lightly dust the sides of the pans with flour and tap out any excess.
2. Into a large bowl, sift flour, black cocoa, unsweetened cocoa, baking powder, baking soda, and salt. Black cocoa powder is very clumpy, so don't skip this sifting step! It also helps achieve a smoother, more "velvety" texture for the cake.

   - 2 cups (260g) all-purpose flour, 1/2 cup (45g) black cocoa powder, 1/2 cup (45g) unsweetened cocoa powder, 2 teaspoons baking powder, 1 teaspoon baking soda, 1/2 teaspoon salt

3. Whisk in the granulated sugar.

   - 1 1/2 cups (300g) granulated sugar

4. Add in the eggs, milk, oil, and vanilla. Whisk until streak free. The batter will be a bit thick at this point.

   - 2 large eggs, 1 cup (240mL) milk, 1/2 cup (120mL) vegetable oil, 2 teaspoons pure vanilla extract

5. In a measuring cup, mix together hot water and espresso powder to dissolve.

   - 1 cup (240mL) boiling water, 1 teaspoon instant espresso powder

6. Pour the hot coffee into the cake batter and whisk to combine. The batter will be very loose now.
7. Divide the batter evenly between your prepared cake pans.
8. Bake the cakes in the center of your preheated oven for 35-40 minutes or until a skewer inserted into the center comes out clean with a few moist crumbs.
9. Cool the cakes for 10 minutes in the pans then flip onto a wire rack. Set aside to cool completely to room temperature before frosting.

Black Buttercream Frosting:

1. Add butter into a large bowl. Using an electric mixer fitted with the paddle attachment, cream on medium speed for 1-2 minutes or until lump free.

   - 1 1/2 cups (340g) unsalted butter

2. Sift in the powdered sugar, black cocoa, and unsweetened cocoa powder. Add in salt, vanilla, and 2 tablespoons of milk.

   - 3 cups (390g) powdered sugar, 1 cup (90g) black cocoa powder, 1/4 teaspoon salt, 1 teaspoon pure vanilla extract, 2-4 tablespoons milk

3. Mix on low speed to dissolve the dry ingredients. Scrape down the bottom and sides of the bowl then whip on medium-high speed for 1-2 minutes or until light and fluffy. If the frosting is too thick, gradually mix in more milk to loosen it. 
4. If the cakes domed in the oven, use a cake leveler or serrated knife to level the tops of the cool cakes. Layer with frosting then frost and decorate the outside however you'd like (I personally just added some candy eyeballs).