Devil's food cake

http://www.marthastewart.com/330175/devils-food-cake-batter

Ingredients

• 3/4 cup plus 3 tablespoons unsweetened Dutch-process cocoa powder
• 1/2 cup plus 2 tablespoons boiling water
• 3 3/4 cups cake flour (not self-rising), sifted
• 1 1/4 teaspoons baking soda
• 3/4 teaspoon coarse salt
• 15 ounces (3 3/4 sticks) unsalted butter, softened
• 2 3/4 cups plus 1 tablespoon sugar
• 1 tablespoon plus 1 teaspoon pure vanilla extract
• 5 large eggs, room temperature
• 1 1/4 cups whole milk

Directions

1. Mix cocoa powder and boiling water in a bowl until smooth. Let cool.
2. Sift flour, baking soda, and salt into a large bowl. Beat butter and sugar with a mixer on medium speed until pale and fluffy, 3 to 4 minutes. Beat in vanilla. Add eggs, 1 at a time, beating well after each addition and scraping bowl as needed.
3. Pour milk into cocoa mixture in a slow, steady stream, whisking until smooth. With mixer on low speed, add flour mixture to butter mixture in 3 additions, alternating with cocoa-milk mixture, starting and ending with flour mixture. Use immediately.