Chocolate Mousse Pie
["1/2 c. butter or margarine, softened", "3/4 c. sugar", "2 (1 oz.) sq. unsweetened chocolate, melted and cooled", "2 eggs", "1 (4 1/2 oz.) carton whipped topping, thawed", "1 (9-inch) baked pastry shell"]
["Cream the butter and sugar until light and fluffy. Stir in cooled chocolate.", "Add eggs, one at a time, beating 5 minutes after each addition. Fold in whipped topping. Spoon mixture into a cooled baked pastry shell. Chill until firm, about 2 hours."]
["butter", "sugar", "unsweetened chocolate", "eggs", "pastry shell"]