In a small saucepan, combine butter and chocolate. Cook and stir over low heat until melted; cool slightly.
Meanwhile, preheat oven to 350. Prepare pastry for a single-crust pie in a 9-inch pie dish.
For filling, in a large bowl, combine eggs, sugar, flour and vanilla. Stir in melted chocolate and the chocolate pieces (and pepper mint extract if substituting.) Pour filling into the pastry-lined pie plate.
Bake in the preheated oven about 55 minutes or until filling isevenly puffed and edge of filling is slightly cracked. Cool on a wire rack about 20 minutes or until slightly warm (center will sink slightly as pie cools.) Top each serving with whipped cream and, if desired, garnish with a mini candy cane or crushed candy canes. Makes 8 servings.