1/3 c. unsalted butter 
1 tsp vanilla 
1/8 tsp salt 
3 c powdered sugar 
2 to 3 tbsp milk 

Cream the butter, vanilla and salt together. Gradually add 1 cup of sugar and beat until well blended. Add 2 tbsp milk and the remaining sugar. Beat until the frosting is of a good spreading consistency. Add the remaining milk a few drops at a time ONLY if the frosting is too thick. This will make enough to fill and frost an 8 or 9 inch round cake, a 9x13 or a tube cake. 

Use These Additions For More Flavors

Almond Frosting 
Substitute ½ tsp Almond extract for vanilla 

Cherry Frosting 
Add 2 tbsp chopped maraschino cherries and 2 drops red food coloring. 

Chocolate Frosting 
Mix in 6 tbsp unsweetened cocoa powder and increase the milk to about 4 tablespoons. 

Coffee Frosting 
Add at least 2 teaspoons instant coffee powder. 

Mocha Frosting 
Blend in ¼ cup unsweetened cocoa powder and 1 teaspoon instant coffee powder and increase milk to 3 or 4 tablespoons 

Lemon Frosting 
Drop the vanilla and use lemon juice in place of the milk. Stir in 1/2 teaspoon grated lemon peel. 

Peanut Butter Frosting 
Drop the butter and substitute creamy peanut butter. Increase the milk to ¼ to 1/3 cup. 

Peppermint Frosting 
Use a few drops of peppermint extract in place of the vanilla.