Mix butter and vanilla until smooth. (I use a hand mixer). Add powdered sugar and a splash of milk. Mix. Add additional milk sparingly until icing reaches your desired consistency.
To make peanut butter icing, follow instructions above, then add ¼-1/2 cup of creamy peanut butter and mix. Add as much or as little peanut butter as you like to taste.
Recipe by Stretching a Buck at https://www.stretchingabuckblog.com/2013/03/how-to-make-a-budget-beach-party-birthday-cake-butter-cream-peanut-butter-icing-recipe.html