Cream softened butter and sugar in a mixer. Add eggs and beat with the mixer. Blend in flour and melted chocolate square. Add vanilla. Pour into a greased pie pan. Bake at 325* for 25 minutes. (Inside will be gooey)
Note: can add another 1/2 to 1 square of chocolate if you like darker chocolate. Garnish with whipped cream. This pie is delicious hot with some vanilla ice cream.