Peanut butter frosting

1/2 C butter, softened
1 C creamy peanut butter
3 T milk
2 C powdered sugar

In a medium bowl, put the butter and peanut butter and mix with an electric mixer. Gradually mix in the sugar. When it gets too thick, add the milk, one tablespoon at a time, until the sugar is mixed in and the frosting is spreadable. Continue beating for about three minutes.