Bring a large pot of salted water to boil for the pasta. Add the pasta when boiling.
Meanwhile, in a large skillet over medium heat, heat the olive oil and the butter. Add the onion and cook until golden. Add the tomato paste and 1/4 cup of water. Add the cream and cook for a couple of minutes. Add the vodka, and salt and pepper to taste, and cook for a few more minutes.
When the pasta is al dente, drain it and add it to the vodka mixture. Mix over medium heat and then serve immediately with a sprinkle of Parmigiano.