Add the pumpkin or squash to the pan and continue cooking for around 10 minutes, stirring occasionally to make sure it doesn’t stick, until the pumpkin or squash starts to soften and turn golden. Tip the sauce back into the large frying pan and add the tomato purée and mascarpone, then bring to a simmer over a low heat and season with salt and pepper to your preferred taste. Heat the oil in a large, deep frying pan and add the onions, fry for 2 minutes, then add the curry paste, lemongrass, cardamom, mustard seeds and garlic and fry for a further 2-3 minutes until fragrant.