1. Melt butter. Stir in cocoa.
2. Alternately add powdered sugar and milk, beating to spreading consistency.
3. Add a small amount of additional milk, if needed.
4. Stir in vanilla.
5. Tip: If the frosting is too thin to spread or pipe, you can put it in the refrigerator to thicken for a little bit, take it out, and then stir so it becomes creamy again.