For the pumpkin purée
- Preheat the oven to 170C. Cut the pumpkin in half horizontally and remove the seeds. Score the flesh, season with salt and pepper, then rub with the cut garlic halves. Lay rosemary sprigs and a garlic half in each pumpkin half. Drizzle with a little olive oil and place on baking trays.
- Roast the pumpkin halves for about 1 hour until tender; the timing will depend on the variety, density and thickness. It is ready when you can effortlessly slip a knife into the thickest part of the flesh. Take out the rosemary and garlic.
- While still hot, scoop out the pumpkin flesh and purée in a blender or food processor.
For the risotto
- Rinse the rice in a sieve, run under cold water and drain well.
- Bring the stock to the boil in a medium saucepan, then add the rice. Lower the heat slightly and simmer for 7 minutes – until almost but not quite al dente.
- Drain immediately, reserving the stock and spread the rice on a tray to cool. Refrigerate until needed.
- About 10-15 minutes before you are ready to serve, heat the olive oil in a medium saucepan. Add the onion with some seasoning and sauté until softened and translucent not browned.
- Stir in the pumpkin purée and cook for another 5 minutes. Meanwhile, bring the reserved stock to the boil in another saucepan.
- Add the pre-cooked rice to the onion and pumpkin, then add just enough hot stock to cover the rice. Quickly bring to a simmer and cook for a few minutes. Taste the rice to see if it is al dente. If, not add a little more stock and cook for a few more minutes.
- Check the seasoning and stir in the butter, followed by the mascarpone and grated Parmesan shaving and serve.