Prepare and chill Pecan Piecrust. Finely shred peel from lemon (reserve lemon for another use). Set aside.
Melt the butter in a straight-sided 12-inch skillet. Add potatoes to hot butter. Cook and stir for 1 minute over medium heat, coating potatoes in butter.
Sprinkle potatoes with sugar; lift and fold potatoes to coat and to dissolve sugar. Cook for 3 to 5 minutes, until caramelized and syrupy, stirring occasionally. (To allow potato slices to brown and caramelize, avoid stirring too often.) Stir in the pecans, lemon peel, nutmeg. Remove from heat; cool.
Preheat oven to 450 degrees F. Roll one portion of the Pecan Piecrust to a 12-inch circle (chill or freeze remaining portion for another use). Fit rolled pastry into a 9-inch pie plate. Trim crust and crimp as desired. Layer with a double-thickness of foil; bake for 8 minutes. Remove foil. Bake for 5 to 6 minutes more or until golden. Reduce oven to 425 degrees F.
Carefully layer cooled potatoes in pie crust, reserving syrup in skillet. Bake for 15 to 20 minutes, until crust is golden and sweet potatoes are tender. Cool slightly, about 15 minutes.
Drizzle reserved syrup on pie. Serve with whipped cream.
In a large bowl combine flour, ground pecans, and salt. Cut in shortening and butter until pea size. Add water, 1 tablespoon at a time, mixing with a fork until all is moistened. Divide in half. Chill for 30 minutes.