How to cook
Beat the butter with a mixer and gradually add the vanilla and powdered sugar, cup by cup. Be sure to get the cream along the walls and bottom and beat it.
After the powdered sugar gets absorbed, add the milk and beat until you get a fluffy and smooth mixture.
Use thus prepared buttercream to cover cakes or stick cake layers together. Keep it in the fridge until it's time to use it.
Optionally, you can color the cream with a little food coloring.