I had a friend over the night after I made this frosting. She swooned as much as I did and described it as "decadent." This might be the single best frosting I have ever tasted. I'm not kidding.
In a medium bowl, beat 1 cup of softened butter with an electric mixer on medium speed until fluffy. Gradually add 2 cups of powdered sugar, beating well. Beat in 2 tablespoons of milk and 2 teaspoons of peppermint extract.
Gradually beat in an additional 3 cups of powdered sugar until smooth. If necessary, beat in additional milk, 1 teaspoon at a time, to achieve spreading consistency.
You will be swooning, too, I promise.