Preheat the oven to 180°C. Put 1 tablespoon of the oil in a small baking dish and add half the pumpkin. Roast in the oven for 30 minutes. Meanwhile, steam the remaining pumpkin for 15 to 20 minutes, then mash. Keep warm.
While the pumpkin is roasting, cook the onion in the remaining oil in a large nonstick frying pan over low heat for 5 minutes or until soft. Add the rice, raise the heat to moderate, and cook for 4 minutes, then add the rosemary.
Heat the stock in a large saucepan until it comes to a gentle simmer. Add 1 ladleful stock to the rice, stirring for about 3 minutes until the rice has absorbed almost all of the liquid.
Continue adding the stock, 1 ladleful at a time, until it has all been absorbed (about 20 to 25 minutes) and the rice is cooked and creamy.
Remove from the heat, season with salt and pepper to taste, then stir in the Parmesan and the mashed pumpkin. Turn the risotto out into a large bowl and serve topped with the cubes of roasted pumpkin.
I never do the 'heat the stock' thing, just make sure its at least room temp - and I don't really add ladle by ladle... I find that this a) takes less time and b) makes rice the exact right texture... I also added a big handful of rocket and a large onion. - 25 Aug 2010
Altered ingredient amounts.
I actually didn't roast the pumpkin, I just cooked it in the stock for about five minutes and I added lots of rocket!! both in the risotto itself and for serving. - 11 Jun 2009