In a large saucepan cook sweet potatoes, covered, in enough boiling salted water to cover for 25 to 35 minutes or until tender. Drain well; return to the same pan. Over low heat, mash potatoes with a potato masher until smooth, allowing any extra moisture to evaporate.

Transfer potatoes to a large bowl. Stir in ricotta cheese, salt, nutmeg (if using), and 1-1/2 cups of the flour. On a well-floured surface, knead in the remaining 1/2 cup flour, kneading for 2 to 3 minutes or until dough forms a soft ball. Divide into 8 pieces. With well-floured hands, roll each piece of dough into a 12-inch-long log (about 1 inch in diameter). Cut logs crosswise into 1-inch pieces. With a floured finger, make a dimple in the center of each piece.

Cook gnocchi, several at a time, in a large pot of boiling salted water for 3 to 4 minutes or until gnocchi rise to the surface of the water. (Do not overcook.) Remove with a slotted spoon; drain on paper towels. Cover to keep warm while cooking remaining gnocchi. If desired, top gnocchi with melted butter, grated Parmesan cheese, and pepper. Makes 16 side dish servings (about 96 gnocchi).

Cool the cooked gnocchi; place in a single layer on a baking sheet. Freeze just until firm. Transfer to a plastic freezer bag; seal, label, and freeze up to 1 month. To use; add to boiling water and cook 1 to 2 minutes or until heated through; drain.