Cream the butter, sugar and egg yolk well. Stir in flour
Pat or spread with an offset spatula into 9x13 greased or lined pan and bake in a 350-degree oven for 25 mins.
While baking, melt the chocolate in a double boiler and spread over bars as soon as they are removed from the oven. Sprinkle bars with nutmeats and toffee bar bits.
Cut into squares and remove from pan as soon as the chocolate is set enough to cut.
This recipe can be doubled and made in ½ sheet pan, just increase baking time to 35 mins.