In a stand mixer with the paddle attachment, cream the room temperature butter on medium high speed until light and fluffy.
Slowly add in the powdered sugar, mixing on LOW speed until fully combined.
Mix in the vanilla extract and two tablespoons of milk. Mix on low speed until combined. If the frosting is too thick, mix in up to two tablespoons of milk. I prefer the consistency of smooth peanut butter when decorating buttercream sugar cookies.
Separate the frosting into various bowls, enough for the various colors you want to dye it. Dye the frosting and add it to the icing bags, using decorating tips.
Decorate the sugar cookies with the buttercream frosting once the sugar cookies have completely cooled. The decorated sugar cookies can be stored on the counter at room temperature for several days or in the freezer for several months.