1/2 c. butter
1/8 tsp. salt
1 lb. (about 4 1/2 c.) unsifted confectioners' sugar
2 egg yolks, unbeaten
1 tsp. vanilla
2 tbsp. milk

Or use 1 whole egg.

Cream butter until soft. Add salt and part of sugar gradually, blending after each addition. then add egg yolks and vanilla; blend well. Add remaining sugar, alternately with milk, until of right consistency to spread, beating after each addition until smooth. (Makes 2 1/2 cups.)