In a large heatproof bowl, microwave the butter and cocoa powder until butter is melted. Beat together with a hand mixer until smooth. Add the vanilla and milk and stir.
Add the confectioners' sugar and stir, slowly at first, until incorporated; then beat on medium speed until frosting is smooth and creamy, about 1 minute. use immediately on cooled brownies, or store, covered at room temperature, for up to a day.
• Use this brownie frosting on my Ultimate Brownies. • Add chopped nuts to the top of the frosting before it sets if desired.• TRY MY OTHER FROSTING RECIPES: