1 (9 inch) pie shell, baked
1/2 c. butter, softened
3/4 c. sugar
1 oz. sq. unsweetened chocolate
1 tsp. vanilla
2 eggs

Melt chocolate and cool. Cream butter. Add sugar gradually and mix well. Blend in chocolate and vanilla. Add eggs, one at a time and beat for 5 minutes. Pour into a baked pie shell. Chill 3 hours or overnight. Top with Cool Whip.