Fry the onion with a pinch of salt for 10–15 minutes until soft and translucent. Add garlic and fry for 1 minute more. Remove from the heat and leave to cool.
Cook the pumpkin in boiling salted water for 10–15 minutes until tender. Blitz with 50ml milk and onions until smooth, gradually adding more milk until the mixture is thick enough to just coat the back of a spoon. Pour into a large frying pan with the tomato purée and mascarpone, and simmer over low heat.
Cook your pasta and drain, reserving a cupful of the cooking water. Toss the pasta with the pumpkin sauce, parmesan and 50–100ml of the reserved water to loosen. Season with extra parmesan. Enjoy!