Mix flour and salt in large bowl. Cut in shortening with pastry blender until mixture resembles coarse cornmeal. Add water, 1 tablespoon at a time, tossing with fork until dough comes together. Loosely shape dough into a ball. Remove one-quarter and shape into disk; wrap in plastic wrap. Shape remaining dough into disk; wrap. Refrigerate both disks 1 hour.
Roll out smaller piece of dough on waxed-paper-lined baking sheet to 1/4-inch thickness. With 1-3/4-inch holly-leaf cutter, cut out about 30 leaves. Reserve scraps. Return leaves to refrigerator. On lightly floured surface, roll out larger piece of dough into 12-inch round. Roll up dough on rolling pin. Unroll into 9-inch pie plate. Trim dough even with edge of rim. Refrigerate pie plate with dough.
Gather scraps together; roll out, 1/4 inch thick, on floured surface. With 1 3/4-inch maple-leaf cutter, cut out about 12 maple leaves. Refrigerate.
Wet small area of edge of pie crust with pastry brush dipped in water. Arrange holly leaves, overlapping, along edge, moistening overlapping portions of leaves. Moisten another small section of edge of pie crust and attach leaves. Continue until edge is covered.
Heat oven to 350 degrees F.
Beat sweet potato, 1 egg, dark-brown sugar and allspice in medium-size bowl until smooth, 2 to 3 minutes. Spread evenly into crust.
Whisk corn syrup, granulated sugar, vanilla and remaining 3 eggs in bowl until well-combined and smooth. Stir in pecans. Pour over sweet potato mixture.
Arrange reserved maple leaves over top of pecan mixture.
Bake in 350 degree F oven 1 hour, until filling is set, crust is light brown. Cool pie on rack. Serve with whipped cream or vanilla ice cream, if desired. Makes 10 servings.