Bring an large pot of generously salted water to a boil. Cook pasta to al dente according to package instructions.
As the pasta cooks, heat olive oil in a large pan over medium heat. Add in the onions and garlic and cook until softened and fragrant, about 3-4 minutes.
Mix in the tomato paste and cook until it starts to thicken and darken in color, about 1-2 minutes.
Mix in the vodka into the tomato mixture and cook for an additional minute. Next, mix in the heavy cream and seasonings (Italian seasoning, red chili flakes, salt and black pepper) into the tomato paste mixture.
Reduce heat to low. Simmer the sauce for 2-3 minutes to thicken slightly. Mix in the Parmesan cheese.
Drain the cooked pasta and reserve 1/2 cup of the pasta water. Add the pasta into the sauce and mix to fully coat. Mix in some of the reserved pasta water a little at a time, as needed, to loosen up the sauce if it is too thick.
Mix the butter into the pasta. Once the butter is fully incorporated, remove the pan from the heat.
Garnish with fresh chopped parsley and serve immediately, then enjoy!