Begin by preparing the pumpkin. Cut it in half, without removing the peel, rub with olive oil and place in a baking dish. Roast in a175°C oven for about 45 minutes or until starting to colour.
Once the pumpkin is tender, remove it from the oven and let cool: then peel and pass through a potato masher.
To make the dough for the pumpkin gnocchi, place the mashed pumpkin on a flat work surface. Add the salt, pepper and nutmeg. Mix together with the egg and flour.
The dough should be soft and light and not stick to your fingertips. Make the gnocchi by first dusting the work surface with a little flour and cutting off a small amount of the gnocchi dough at a time. Roll this into a log and cut into small cylindrical pieces. Cook the gnocchi in a large pot of boiling salted water. While the gnocchi are cooking, prepare the sauce: in a skillet, melt the butter with a couple of fresh sage leaves.
Add a tablespoon of cooking water to the butter and stir to make a sauce. Once the gnocchi rise to the top of the pot, remove them using a slotted spoon. Carefully toss them in the melted butter. Finish with grated Parmigiano Reggiano.