Thumbprint Cookies

1 c. butter, softened
2/3 c. sugar
2 egg yolks
1/2 t. vanilla
2 1/4 c. flour
1/2 t. salt
chocolate frosting

Cream butter; gradually add sugar, beating until light and fluffy. Add egg yolks, one at a time, beating well after each addition. Stir in vanilla. Combine flour and salt; add to creamed mixture, mixing well. Chill. Roll dough into 1" balls; place about 2" apart on ungreased cookie sheets. Press thumb into each ball of dough, leaving an indentation. (Can use melon baller.) Bake at 300° for 18 to 20 minutes; do not brown. Allow to cool on wire racks. Place about 1/2 t. chocolate frosting in each indentation

Makes 3 1/2 dozen.

Chocolate Frosting

1 c. sugar
1/4 c. cocoa
1/4 c. milk
1/4 c. butter
1/2 t. vanilla

Combine sugar, cocoa, and milk in heavy saucepan. Bring to boil, and boil 1 1/2 to 2 minutes, stirring constantly. Remove from heat; stir in butter and vanilla. Beat until mixture is of spreading consistency.