Beat butter and shortening on high for about 5 minutes.
Turn down your mixer to slowest speed and slowly add sugar, vanilla.
Turn mixer back to medium speed and **add milk /one tablespoon at a time until you reach your desired consistency. beat for about 3-5 more minutes the less milk, the stiffer the batter- which is best if you are cake decorating if you get your frosting too thin, add powdered sugar to stiffen back up.
