For filling, in a bowl lightly beat eggs just until combined. Stir in corn syrup, sugar, and melted margarine. Mix well. Stir in black walnuts. Set filling aside.
Mix all-purpose flour and salt. Cut in shortening or lard until pieces are the size of small peas. Sprinkle cold water, 1 tablespoon at a time, over mixture, tossing with a fork after each addition until all is moistened. Form dough into a ball. On a lightly floured surface, slightly flatten dough. Roll dough from center to edges, forming a 12-inch circle. Wrap pastry around the rolling pin. Unroll onto a 9-inch pie plate. Ease pastry into pie plate, being careful not to stretch it. Trim pastry to 1/2 inch beyond edge of plate. Fold under extra pastry; crimp edge. Sprinkle chocolate pieces over bottom of pastry shell. With pastry shell on oven rack, pour filling into shell.
To prevent over browning, cover edge of pie with foil. Bake in a 350 degree F oven 20 minutes. Remove foil. Bake 20 to 25 minutes more or until a knife inserted near center of pie comes out clean. Cool. Serve or store, covered, in the refrigerator up to 24 hours. Dollop with whipped cream before serving, if desired. Makes 8 servings.