Preheat the oven to 180°C. Lay the pancetta onto a baking tray and cook for 10-12 minutes or until crisp. Set aside to cool and break into small pieces. In a large heavy-based saucepan heat the olive oil. Add the onion and pumpkin and saute gently for 5 minutes. Stir in the rice to coat and pour in the wine. Reduce until all liquid is absorbed. Add the stock in 4 batches, stirring constantly and allowing all of the liquid to absorb before adding more. When all of the stock has been absorbed add the pancetta, mascarpone, thyme and half the parmesan. Season to taste and serve topped with the remaining parmesan.