Toffee Bars

1 cup butter
1 cup packed brown sugar
1 egg
1 t vanilla
2 cups flour
1 6oz pkg semi-sweet chocolate pieces

Beat butter 30 seconds, add brown sugar and beat until fluffy. Add egg yolk and vanilla, beat well. Gradually add flour to beaten mixture, beating constantly. Press evenly in an ungreased 15 x 10 x 1-inch baking pan. Bake 350 for 15 - 18 minutes. Immediately sprinkle chocolate pieces over top and let stand till softened, then spread evenly. Sprinkle with finely chopped nuts.