1. Unroll piecrust on a lightly floured surface. Sprinkle with cornmeal and chopped fresh rosemary. Lightly roll cornmeal and rosemary into crust. Fit into a 9-inch pie plate according to package directions. Fold edges under; crimp. Chill 30 minutes.
2. Preheat oven to 400°. Bake crust 20 minutes, shielding edges with aluminum foil to prevent excessive browning. Cool completely on a wire rack (about 1 hour).
3. Meanwhile, prepare Filling: Bake sweet potatoes at 400° on a baking sheet 50 to 55 minutes or until tender. Let stand 5 minutes. Cut potatoes in half lengthwise; scoop out pulp into a bowl. Mash pulp. Discard skins.
4. Whisk together eggs and granulated sugar until well blended. Add milk, next 6 ingredients, and sweet potato pulp, stirring until blended. Pour mixture into baked crust.
5. Bake at 400° for 20 minutes. Reduce heat to 325°, and bake 20 to 25 minutes or until center is set. Let cool completely on a wire rack (about 1 hour).