cake

•2 cups cake flour
•3/4 cup natural unsweetened cocoa powder
•1 1/2 teaspoons baking soda
•3/4 teaspoon salt
•3/4 cup (1 1/2 sticks) unsalted butter, room temperature
•2 cups (packed) golden brown sugar
•3 large eggs
•1 1/2 teaspoons vanilla extract
•1 cup buttermilk
•4 teaspoons instant espresso powder dissolved in 3/4 cup hot water

frosting

•1/3 cup natural unsweetened cocoa powder
•1 tablespoon instant espresso powder
•1 1/2 cups chilled heavy whipping cream, divided
•1 1/3 cups sugar
•28-ounce containers chilled mascarpone cheese
•Bittersweet chocolate curls (optional)