Peel sweet potatoes; cut off woody portions and ends. Cut sweet potatoes into quarters. In a covered large saucepan cook sweet potatoes in enough boiling salted water to cover for 25 to 30 minutes or until tender. Drain sweet potatoes; transfer to a large bowl. Using a potato masher or electric mixer, mash sweet potatoes until smooth (you should have 1 1/2 cups mashed sweet potatoes). Add 1/4 cup butter to hot potatoes, stirring until melted.
Preheat oven to 375 degrees F. Prepare Cornmeal Pastry. On a lightly floured surface, use your hands to slightly flatten pastry. Roll pastry from center to edges into a circle about 12 inches in diameter. Wrap pastry circle around the rolling pin. Unroll into a 9-inch pie plate. Ease pastry into pie plate without stretching it. Trim pastry to 1/2 inch beyond edge of pie plate. Fold under extra pastry. Crimp edge high to keep filling from bubbling over. Do not prick pastry.
For filling, stir 1/2 cup brown sugar, orange peel, 1 teaspoon cinnamon, ginger, and 1/4 teaspoon nutmeg into mashed sweet potatoes. Stir in eggs and half-and-half. Place the pastry-lined pie plate on the oven rack. Carefully pour filling into pastry. Cover edge of pie loosely with foil. Bake for 30 minutes.
Meanwhile, for topping, in a small bowl stir together flour, 1/4 cup brown sugar, 1/8 teaspoon cinnamon, and 1/8 teaspoon nutmeg. Using a pastry blender, cut in 2 tablespoons butter until mixture resembles coarse crumbs. Stir in hazelnuts.
Remove foil from pie. Sprinkle topping over pie. Bake about 20 minutes more or until a knife inserted near the center comes out clean. Cool on a wire rack for at least 1 hour. Cover and chill within 2 hours.
In a medium bowl, stir together all-purpose flour; yellow cornmeal; sugar; and salt. Using a pastry blender, cut in shortening until pieces are pea-size. Sprinkle 1 tablespoon cold water over part of the mixture; gently toss with a fork. Repeat moistening dough, using 1 tablespoon cold water at a time until all the dough is moistened. Form into a ball.
On a lightly floured surface, use your hands to slightly flatten dough. Roll dough from center to edge into a 12-inch circle. To transfer pastry, wrap it around the rolling pin. Unroll pastry into a 9-inch pie plate; ease pasty into pie plate, being careful not to stretch pastry. Trim to 1/2 inch beyond edge of plate. Fold under extra pastry; crimp edge high. Do not prick.