Heat the oven to 200 C / 390 F. Halve the pumpkin, scoop out the seeds, and roast cut-side down on a sheet pan (33 x 46 cm / 13 x 18 inch) for 40 to 45 minutes, until a knife slides in with no resistance.

Meanwhile, boil the potatoes whole and skin-on in salted water for 25 to 30 minutes, until tender. Drain, peel while still hot, and pass through a potato ricer into a large bowl.

Scoop out about 350 g of the roasted pumpkin flesh and pass it through the ricer into the same bowl as the potato. Spread the mixture on a clean kitchen towel and let it sit for 10 minutes to dry out excess moisture.

Return the dried mixture to the bowl. Add the egg yolk, grated parmesan, nutmeg, and salt, and mix with a fork until combined.

Add the flour a little at a time, folding gently, until the dough just holds together and feels slightly tacky but not sticky. Stop as soon as it comes together; extra flour makes the gnocchi heavy.

Turn the dough onto a floured surface and divide into 4 pieces. Roll each into a rope about 2 cm / 3/4 inch thick, then cut into 2 cm pieces. Roll each piece over a fork if you want ridges.

Bring a 5-quart / 4.7 L pot of salted water to a boil. Cook the gnocchi in batches of 20 to 25 so the water stays at a rolling boil, until they float to the surface, 2 to 3 minutes. Lift out with a slotted spoon.

While the gnocchi cook, melt the butter in a 12-inch / 30 cm skillet over medium heat. Swirl the pan for 3 to 4 minutes until the butter turns amber and smells nutty. Watch closely, it can burn within seconds of browning.

Add the sage leaves to the browned butter and fry for 30 seconds, until crisp.

Add the drained gnocchi straight into the skillet and toss gently for 1 to 2 minutes to coat in the butter.

Divide among plates, top with shaved parmesan and black pepper, and serve right away.