FOR THE CAKE: – 3/4 cup (90g) all-purpose flour – 1/4 cup (21g) unsweetened cocoa powder – 1/4 teaspoon baking powder – 1/8 teaspoon baking soda – 1/8 teaspoon salt – 1/4 cup (56g) unsalted butter, softened – 1/4 cup (50g) granulated sugar – 1/4 cup (50g) firmly packed light brown sugar – 1 large egg – 1/4 teaspoon vanilla extract – 1/4 cup + 1 tablespoon (75ml) buttermilk FOR THE FROSTING: – 1/3 cup (75g) unsalted butter, softened – 1/3 cup (36g) confectioners’ sugar, sifted – 1/4 teaspoon vanilla extract – 1/3 cup (43g) marshmallow creme (such as Marshmallow Fluff) – chocolate sprinkles, for garnish