Cream 3/4 cup butter. Add 1 cup sugar; cream well. Blend in 3 (1 ounce) squares unsweetened chocolate (melted and cooled) and 1 1/2 teaspoons vanilla. Add 3 eggs, one at a time, beating 5 minutes after each egg on medium speed. Turn into a baked and cooled 8 or 9 inch pie shell. Chill well. Top with whipped cream and chopped nuts when serving.