In a mixing bowl, cream the butter until it is light and fluffy. Add the salt. Add ½ cup of powdered sugar at a time, mixing well in between each addition, until you reach 2 cups. Scrape the sides of the bowl, with a spatula. Mix in the vanilla extract. If your frosting isn't a very spreadable consistency, add 1 tbsp of milk/heavy cream and mix well. If it is still too thick, add 1 tbsp of the liquid at a time, mixing well in between each addition, until you reach a smooth spreadable consistency. If you would like colorful frosting, add a couple drops of food coloring and mix well.