In the top of a double boiler over simmering water melt the semisweet and unsweetened chocolate pieces along with the butter, stirring often.
Remove the pan from the water.
In a large mixing bowl beat the eggs, sugar and corn syrup, blending well
Carefully beat in the warm chocolate. Add the vanilla, blending well. Gently stir in the pecan pieces.
Pour the filling into the prepared crust.
Bake at 400 degrees for 5 minutes. Reduce the temperature to 350 and bake for 30 minutes.
The pie will puff up in the center.
Remove the pan from the oven and cool for 1 hour before serving. Top with whipped cream.