To roast the squash
Cut the squash (with the skin on) into approx. 3 cm slices. In a large bowl, mix the squash with the oil and salt, transfer to a baking tray lined with baking paper. Roast for approx. 30 mins. in the centre of an oven preheated to 200°C. Pass the squash (with the skin on) through a food mill while still hot (yields approx. 400 g), leave the squash puree to cool.
Add the flour, parmesan and egg yolk to the squash puree, season and mix quickly to form a smooth dough.
To shape the gnocchi
On a lightly floured surface, shape the gnocchi mixture into rolls (each approx. 1.5 cm in diameter), cut the rolls into pieces approx. 1 cm long.
Using your thumb, roll them over the prongs of a fork to create a pattern. Place the gnocchi on a floured tea towel or plate.
To cook the gnocchi
Cook the gnocchi in batches in gently simmering salted water for approx. 5 mins. until they float to the surface. Remove the gnocchi with a slotted spoon and drain.
Heat the butter in a non-stick frying pan, add the gnocchi and sage, fry for approx. 5 mins. Plate up the gnocchi, serve with parmesan.