Pierce sweet potatoes with a fork. Microwave on high (100 percent) power for 10 to 12 minutes or until tender, turning sweet potatoes over halfway through cooking. Cut sweet potatoes open; cool completely.
In a medium bowl, stir together flour, granulated sugar, the 1 teaspoon allspice, and 1/4 teaspoon salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon of the ice water over part of the flour mixture; gently toss with a fork. Push moistened dough to side of bowl. Repeat moistening flour mixture, using 1 tablespoon of the remaining ice water at a time, until all the flour mixture is moistened. Form dough into a ball. On a lightly floured surface, use your hands to slightly flatten dough. Roll dough from center to edge into a circle about 12 inches in diameter.
Transfer dough to a 9-inch pie plate without stretching it. Trim dough to 1/2 inch beyond edge of pie plate. Fold under extra dough. Crimp edge as desired. Do not prick dough.
Preheat oven to 375 degrees F.
Scrape flesh from cooled sweet potatoes into a medium bowl; mash until smooth. Measure enough mashed sweet potato to equal 1-1/2 cups. In another medium bowl, combine eggs, brown sugar, whipping cream, allspice, orange peel, vanilla, salt, and mashed sweet potato. Place pastry-lined pie plate on oven rack. Carefully pour filling into pastry shell.
To prevent overbrowning, cover edge of pie with foil. Carefully transfer pie to oven rack. Bake for 25 minutes. Remove foil. Bake for 20 to 25 minutes more or until knife inserted near the center comes out clean and the edge is puffed. Cool on a wire rack. Cover and refrigerate pie within 2 hours.
If desired, serve pie with whipped cream and sliced kumquats. Makes 8 servings.