01 - Preheat oven to 400°F (200°C). Pierce sweet potatoes with a fork, place on baking tray, and roast for 40–45 minutes until tender. Cool slightly, peel, and mash until smooth.
02 - Transfer mashed sweet potato into a large mixing bowl. Add egg, fine sea salt, black pepper, and nutmeg (if using); mix until blended.
03 - Gradually fold in all-purpose flour, stirring until a soft, slightly sticky dough forms. Use just enough flour to achieve a workable texture.
04 - Dust work surface with flour. Divide dough into four portions. Roll each into ropes approximately ¾ inch thick, then cut into ¾ inch pieces. Optionally, shape using a fork for classic ridges.
05 - Bring a large saucepan of salted water to a gentle boil. Working in batches, add gnocchi pieces; cook until they float (about 2–3 minutes). Remove with a slotted spoon and drain thoroughly.
06 - Melt unsalted butter in a large skillet over medium heat. Add sage leaves and cook, swirling gently, until butter turns golden and sage crisps, 2–3 minutes.
07 - Transfer drained gnocchi to skillet. Toss gently to coat evenly in sage butter. Season with flaky sea salt and additional black pepper as desired.
08 - Plate immediately and finish with a generous sprinkle of freshly grated Parmesan cheese.