Apple (or Rhubarb) Bars Recipe

Mix together first three ingredients as for pie crust. Beat 1 egg yolk and add milk to make 1/2 C. Add to flour mixture. Divide in half and roll out to fit bottom of 9x13 pan. Spread filling on bottom crust. Roll out rest of dough for top. Bake 30 minutes or until golden brown at 400°. Frost while still warm with thin mixture of powdered sugar and milk. Freezes well. Double everything and use a jelly roll pan.