01 - Preheat oven to 400°F. Pierce sweet potatoes with a fork, place on a baking sheet, and bake until tender, about 45 to 60 minutes. Allow to cool, then peel and mash until smooth. Measure out 2 cups mashed sweet potato for use.
02 - In a large mixing bowl, combine mashed sweet potato, egg, salt, black pepper, and nutmeg. Gradually add flour, mixing until dough is soft and slightly sticky. Do not overmix.
03 - Turn dough onto a floured surface. Divide into four equal portions. Roll each piece into a rope about 3/4 inch thick. Cut into 1-inch pieces. If desired, roll each piece over a fork to create ridges.
04 - Bring a large pot of salted water to a gentle boil. Working in batches, drop gnocchi pieces into the water. When they float to the surface after 2 to 3 minutes, remove using a slotted spoon and set aside.
05 - In a large skillet over medium heat, melt butter. Add sage leaves and cook until butter turns golden brown and sage is crispy, 3 to 4 minutes. Remove sage leaves and reserve.
06 - Add cooked gnocchi to the skillet with brown butter. Toss gently until gnocchi are heated through and lightly golden, about 2 to 3 minutes.
07 - Transfer gnocchi to serving plates. Garnish with crispy sage and freshly grated Parmesan. Serve immediately.