Brown Sugar Shortbread Puffs

1 cup firmly packed brown sugar
1 1/4 cups butter or margarine, softened
1 teaspoon vanilla extract
1 egg yolk
2 1/4 cups all-purpose flour

Heat oven to 350 degrees F.

In large bowl, beat brown sugar and margarine until light and fluffy. Add vanilla extract and egg yolk; blend well. Add flour; stir until mixture forms a smooth dough. Drop dough by rounded teaspoonsful 2 inches apart onto ungreased cookie sheets. Bake for 10 to 15 minutes or until lightly browned and set.