For filling, In a heavy saucepan, melt butter and unsweetened chocolate over low heat, stirring frequently. Cool 20 minutes.
Prepare, roll out pastry. Line a 9 inch pie plate with pastry, trim and crimp edge.
In mixing bowl, mix eggs, sugar, flour and vanilla. Stir in chocolate mixture and chocolate pieces. Pour into pie shell.
Bake pie in 350 degree oven for about 55 minutes or until filling is evenly puffed and edges of filling are slightly craked. Cool on wire rack, center will sink slightly as pie cools. Serve with whipped cream and if you like shaved candies. I have used a candy cane and chopped into small pieces to sprinkle on top of whipped cream.
Note: if you can not find the mint flavored chocolate chips, use regular chocolate chips and add 1/2 tsp peppermint extract to the batter.