Preheat your oven to 200°C (400°F). Cut the pumpkin in half, scoop out the seeds, and place it cut-side down on a baking sheet. Roast until tender and soft, about 40 minutes, until the flesh is easily pierced with a fork.
Once roasted, let the pumpkin cool slightly, then scoop out the flesh and mash it until smooth. Set aside to cool for a few minutes; the mash should be warm but not hot.
In a mixing bowl, combine the warm pumpkin with the beaten egg, nutmeg, and a pinch of salt. Stir until well blended and the mixture is smooth.
Add the all-purpose flour to the pumpkin mixture, gradually folding it in until a soft dough forms. Be careful not to overmix; just combine until incorporated.
Lightly flour a clean surface and turn out the dough. Gently knead it a few times just to bring it together, then divide it into four equal portions.
Roll each portion into a long rope about 2 cm (3/4 inch) thick. Use your hands or a floured rolling pin to shape it evenly.
Cut each rope into 2 cm (3/4 inch) pieces. Lightly press each piece with a fork or gnocchi board to create ridges, which help hold the sauce and add texture.
Bring a large pot of salted water to a gentle boil. Carefully drop the gnocchi into the water, working in batches if necessary.
Cook the gnocchi until they float to the surface, about 2-3 minutes. Use a slotted spoon to lift them out gently and set aside.
Meanwhile, melt the butter in a skillet over medium heat. Add the sage leaves and cook until fragrant and slightly crispy, about 2 minutes, watching carefully so it doesn’t burn.
Gently toss the cooked gnocchi in the sage butter until evenly coated. Serve immediately with a sprinkle of fresh sage if desired.