Preheat oven to 180°C.
Scoop the flesh out of the pumpkin, remove the seeds and finely dice the flesh. Wrap in aluminum foil and cook in the oven at 180°C degrees for 30 minutes.
Meanwhile, peel and chop the onion and saute gently using 1 tablespoon butter. Add the rice and saute gently until translucent. Then gradually add the vegetable stock, stirring frequently. The rice should be cooked when it has taken up all the stock (about 30 minutes cooking time).
10 minutes before the end of the cooking time carefully stir in the diced pumpkin. Before serving mix in the rest of the butter and the Parmesan cheese and season to taste with salt and pepper.
If you wish, serve the risotto in the hollowed-out pumpkin and garnish with sage leaves. You may want to heat the hollowed-out pumpkin before serving. If so, place halved pumpkin shells upside down on greased baking sheet. Bake at 120°C for 15 minutes until warmed through.