French Silk Pie

1 stick butter
3/4 cup sugar
1 1/2 squares unsweetened chocolate
1 tsp. vanilla
2 eggs
1 baked pie shell, cooled
1 pkg. Cool Whip

Cream the butter and sugar in a bowl. Melt the chocolate and stir into creamed mixture. Add vanilla. Add one egg at a time and beat with electric mixer for 5 minutes after each egg. Pour into pie shell and top with cool whip. Chill.