Start by creaming together butter and sour cream, vanilla, and salt. Slowly add powdered sugar. When it gets so thick its not frosting-like, add a splash of milk. Alternate this process until your frosting is the desired consistency. Add 1 drop of red food coloring and whip on high for 1 minute.
Keep cookies in a sealed container until they are ready to serve. The magic of a Swig Sugar Cookie is that the cookies are cold and the frosting is room temperature. Frost right before serving.