Combine all the ingredients together using a mixer or sturdy spatula. {I use a spatula, so I don't have much to clean after}. Add more milk if you want a thinner consistency. Add more powdered sugar if you want a thicker consistency.

Make sure to cover when not in use, so it doesn't dry out. I keep it covered in a container in the refrigerator (since there is butter and milk in it). If you need to, just add a little more milk to make it spreadable again.