1/2 cup butter or margarine
7 tablespoons root beer (not diet)
3 tablespoons unsweetened cocoa
1 (16-ounce) package powdered sugar
1 teaspoon vanilla extract
Bring first 3 ingredients to a boil in a large saucepan over medium heat, stirring until butter melts. Remove from heat; whisk in powdered sugar and vanilla until smooth.