Cream butter and sugar, beat in egg and vanilla. Blend in flour. Press smoothly into foil-lined, greased 13×9 pan. Prick. Chill 1 hour. Bake at 350 degrees for 10 minutes, then at 325 for 15 minutes.
Combine. Boil on medium high heat for four minutes, stirring continuously.
Add to above and heat. Spread over hot crust. Continue to bake at 300 degrees until bubbly, about 15-20 minutes. Cool thoroughly, remove foil, place on cutting board to cut with heavy, sharp knife.