2 cups confectioners’ sugar
1/2 cup unsweetened cocoa powder
6 large marshmallows
4 tablespoons (1/2 stick) butter
1/3 cup plus 1 tablespoon milk
1 teaspoon pure vanilla extract
Sift the sugar and cocoa powder together into a large mixing bowl. Set aside.
Place the marshmallows, butter, and milk in a medium-size heavy saucepan over low heat. Stir until the marshmallows are melted, 3 to 4 minutes. Remove the pan from the heat. Pour the confectioners’ sugar and cocoa mixture over the marshmallow mixture. Add the vanilla and stir until the frosting is smooth and satiny.
Use at once to frost the top of the cake of your choice.