1/2 cup butter
1/2 cup unsweetened cocoa powder
2 cups powdered sugar
1/4 - 1/2 cup cream or milk
1 teaspoon vanilla
Place the butter in a small microwave-safe bowl and microwave on high until melted. Add cocoa powder and stir until combined.
Add the powdered sugar and 1/4 cup cream (or milk) and vanilla and stir until smooth. Add additional cream or milk until frosting reaches desired consistency.