Bring a pot of water to boil. When it's boiling, add salt. Throw the pasta in and cook until it's just before al dente – this is important because the pasta will finish cooking in the sauce.
Just before the water comes to a boil, add the olive oil to a pan. When the olive oil is heated through, add the onion. Cook until golden and fragrant.
Add in the prosciutto and let it cook a few minutes. Add in the chili flakes.
Add the tomato paste and let it cook for a few minutes, stirring with a wooden spoon.
Add the vodka, and let the alcohol cook off, a few minutes.
Add the mascarpone. Add pasta cooking water so that a sauce forms with the mascarpone. If the pasta is not cooked by this point, turn the heat down to low.
Add the pasta to the sauce, along with a bit more pasta water if needed, and let the pasta continue cooking in the sauce, until al dente.
Add parmigiano reggiano, stir one last time. Plate and top with parsley if desired.