Cream butter and brown sugar. Add the egg yolk to mixture and beat well. Blend in the flour to form a stiff dough. Roll into marble sized balls on a greased cookie sheet. Flatten with a glass dipped in sugar. Bake at 350 degrees for 7-9 minutes until golden brown.
Melt and brown the butter in a saucepan. Blend int he powdered sugar. Add vanilla and cream and beat until smooth.