1 stick butter
1 Ib powdered sugar
pinch salt (up to 1/4 tsp if using unsalted butter)
1/2 tsp vanilla
1 or more TBS milk

Cream butter until soft and smooth.
Add sugar a little at a time.
Blend until all lumps are gone.
Add salt & vanilla, and enough milk to make consistency you like.
Add milk a little at a time.
If you are making a lot it frosting, you may have as add milk as you add the sugar, if it gets too thick and stiff.