Food Network and Betty Crocker provide easy-to-follow recipes for brownie frosting. The Food Network version uses coconut as a base, while the Betty Crock recipe uses cream cheese.
To make Food Network's brownie frosting recipe, combine 1 cup evaporated milk, 1 cup sugar and 4 egg yolks in a saucepan. Heat, and stir with a wire whisk until the yolks are evenly mixed. Add 1/2 cup butter and melt. Bring the mixture to a simmer, and cook for 12 to 15 minutes, or until it thickens, stirring constantly. Add 10-ounces fresh or thawed frozen grated coconut, 1 1/2 cups nuts of your choice, and 1 teaspoon vanilla extract, and let cool. The recipe yields 4 cups. Frost when the brownies are completely cool.
To make Betty Crocker's brownie frosting recipe, beat 3 ounces softened cream cheese, 1 tablespoon milk, 1 teaspoon vanilla and a dash of salt. Add 2 ounces unsweetened baking chocolate that has been melted and cooled. Gradually add in 2 1/2 cups powdered sugar one spoonful at a time, consistently beating the mixture until the frosting is smooth and spreadable. If it is too thick, stir in more milk, 1 teaspoon at a time. Frost when the brownies are completely cool.