Dark-Chocolate Cake with Ganache Frosting

INGREDIENTS 1 cup (2 sticks) unsaltedbutter, room temperature, plus more for pans 1/2 cup unsweetened Dutch-processcocoa(spooned and leveled), plus more for pans 2 cups all-purpose flour (spooned and leveled) 1/2 teaspoon baking powder 1/2 teaspoon baking soda 1/2 teaspoon salt 1 1/2 cups packed light-brownsugar 2 large eggs plus 2 largeegg yolks, room temperature 6 ounces bittersweetchocolate, melted 1 teaspoon pure vanilla extract 1 cup low-fat buttermilk Dark-Chocolate Ganache

DIRECTIONS1. STEP 1Preheat oven to 350.Buttertwo 8-inch roundcake pans; dust withcocoa, tapping out excess. Line bottom of each pan with a round ofparchmentpaper; set aside. In a medium bowl, whisk together flour, cocoa, baking powder, baking soda, and salt; set aside.IN THIS STEP: How to Make a Parchment-Paper Round2. STEP 2In a large bowl, using an electric mixer, beatbutterandsugaruntil light and fluffy. Add eggs and yolks, one at a time, beating well after each addition; beat inchocolateand vanilla. With mixer on low, alternately add flour mixture in three parts and buttermilk in two, beginning and ending with flour mixture.3. STEP 3Divide batter between prepared pans; smooth tops. Bake until a toothpick inserted in center of a cake comes outclean, 40 to 45 minutes. Cool in pans 15 minutes; run a knife around edge of each pan, and invertcakesonto a wire rack to cool completely.IN THIS STEP: How to Make Perfect Cakes4. STEP 4Set a rimmed baking sheet upside down on a work surface. Place one cake on sheet, and spread top with 1/3 ofganache. Place second cake on top, and spread remaining ganache over top and sides of cake. Using two wide metal spatulas, carefully transfer frosted cake to a serving platter.