In a large saucepan, heat the olive oil and add in the onion, garlic and chilli flakes. Cook on a medium heat for 5-8 minutes until the onions are soft and golden, but not browned, stirring occasionally.
Add the tomato paste and keep cooking for 5 minutes on a low-medium heat, so that the tomato paste coats the onion and garlic and absorbs their flavour.
Move the pan to the smallest ring on the hob and set it on a really low heat to avoid lighting the alchohol as you add it. Once you have added the vodka, leave it to bubble for a few minutes to allow the alcohol to evaporate, then add 3 1/2 tablespoons of water and the mascarpone. Stir until the cheese has completely melted into the sauce, then take it off the heat.
Bring a large pot of water to boil, add in salt and the malloreddus pasta. Cook for 3-4 minutes, then drain the pasta, reserving a small jugful of cooking water in case you need to loosen the sauce.
Put the sauce back on a medium-low heat, transfer the pasta into the pan and combine it all together. Stir in the butter, if using. Scatter the parmesan all over the pasta and mix it in. Taste it and add more seasoning if desired or more pasta water to loosen the sauce. Divide between four bowls and enjoy.