Preheat oven to 350°F. Spray three 8-inch round cake pans with nonstick spray and add a parchment circle to the bottoms. Set aside.
Whisk the flour, sugar, cocoa powder, baking soda, salt, and baking powder in the bowl of a stand mixer.
3 cups all-purpose flour, 3 cups granulated sugar, 1 cup unsweetened cocoa powder, 1 tablespoon baking soda, 1 teaspoon kosher salt, 1 teaspoon baking powder
Add the eggs, milk, oil, and vanilla to the mixing bowl. Using the paddle attachment, beat the mixture on medium-high speed for 2 minutes, then stir in the boiling water.
3 large eggs, 1½ cups milk, 1 cup vegetable oil, 2 teaspoons pure vanilla extract, 1½ cups water
Divide the batter equally between the 3 cake pans (about 703 grams per pan).
Bake for 35-45 minutes, until the cake springs back when touched gently.
Let a cake cool in the pan for 5 minutes, then transfer to a cooling rack and allow it to cool completely.