Cream the butter and sugar together using the paddle attachment in a stand mixer at medium speed, until light and fluffy.
Next, beat in the vanilla and scrape down the sides of the bowl.
Add the powdered sugar a cup at a time, turning the speed to low with each new addition then returning to the medium setting. Stop often to scrape down the sides.
If the mixture is a little too dry for your needs, add milk until it reaches the desired texture.