01 - Preheat oven to 400°F. Prick sweet potatoes with a fork, place on a baking tray, and roast for 40–45 minutes or until very tender. Allow to cool slightly, then peel and mash until smooth.
02 - Transfer mashed sweet potato to a large mixing bowl. Add egg, sea salt, black pepper, and nutmeg if using. Mix thoroughly.
03 - Gradually incorporate flour, stirring until a soft, slightly sticky dough develops. Add just enough flour to achieve a workable consistency.
04 - Dust work surface with flour. Divide dough into four pieces. Roll each into a rope approximately ¾ inch thick. Slice ropes into ¾ inch segments. Optionally, roll each gnocchi over the tines of a fork to create ridges.
05 - Bring a large saucepan of salted water to a gentle boil. Working in batches, add gnocchi and cook until they float to the surface, about 2–3 minutes. Remove with a slotted spoon and drain well.
06 - Heat unsalted butter in a large skillet over medium heat. Add sage leaves and cook, swirling pan, until butter is golden and nutty and sage is crisp, around 2–3 minutes.
07 - Add drained gnocchi to the skillet. Toss gently to coat with sage butter. Season with flaky sea salt and additional black pepper as desired.
08 - Arrange gnocchi on plates and garnish with freshly grated Parmesan. Serve immediately.