Moist Devil's Food Cake with Mrs. Milman's Chocolate Frosting

• 3/4 cup unsweetened Dutch-process cocoa powder, plus more for pans
• 1/2 cup boiling water
• 3 cups sifted cake flour (not self-rising)
• 1 teaspoon baking soda
• 1/2 teaspoon salt
• 2 1/4 cups sugar
• 4 large eggs, lightly beaten
• 1 tablespoon pure vanilla extract
• 1 cup whole milk
• Mrs. Milman's Chocolate Frosting

1 1/2 cups (3 sticks) unsalted butter, softened, plus more for pans

Directions

1. Preheat oven to 350 degrees. Butter three 8-inch round cake pans. Line bottoms with parchment; butter parchment. Dust with cocoa powder; tap out excess. Set aside. Sift cocoa powder into a medium bowl; whisk in boiling water. Set aside to cool.
2. Sift together flour, baking soda, and salt into a large bowl; set aside. Put butter into the bowl of an electric mixer fitted with the paddle attachment. Mix on low speed until creamy. Gradually mix in sugar until pale and fluffy, 3 to 4 minutes. Add eggs, a bit at a time, mixing well between each addition; mix until well blended. Mix in vanilla.
3. Whisk milk into reserved cocoa mixture. With mixer on low speed, add flour mixture to butter mixture in 3 batches, alternating with the cocoa mixture.
4. Divide batter evenly among prepared pans; smooth tops with an offset spatula. Bake, rotating pan halfway through, until a cake tester inserted into centers comes out clean, 35 to 45 minutes. Let cool in pans on wire racks 15 minutes. Turn out cakes onto racks; remove parchment and re-invert. Let cool completely.
5. Using a serrated knife, trim tops of cakes to make level. Place four strips of parchment paper around perimeter of a serving plate or lazy Susan. Place the first layer on the cake plate. Spread the top of the first layer with 1 1/2 cups of frosting. Place the second layer on top and repeat process with another 1 1/2 cups of frosting. Place the remaining layer on top of the second layer, bottom side up. Spread entire cake with remaining 3 cups frosting.

Source: Martha Stewart Living