Cook the pasta according to pack instructions, reserving one-third cup of the cooking water. Preheat the grill to high.
While the grill heats up, pour the olive oil into a large ovenproof saucepan set over a medium heat. Cook the onion for 5-6 minutes until soft and translucent, add the garlic and thyme and cook for a further minute.
Turn the pan to a low heat and stir through the cream and mascarpone. Pour in the reserved cooking water and bring the sauce to a gentle simmer for 3-4 minutes. Add the cooked pasta to the pan then stir through the lemon juice, Parmesan and chives.
Place the pan under the grill for 6-8 minutes, or until golden brown. Serve topped with lemon zest, extra thyme leaves and Parmesan
