Boil rigatoni in a pot of heavily salted water. Reserve 1/2 cup of pasta water before you drain the pasta.
Add butter to a saute pan over medium-low heat. When butter is warm and melted, add diced onions to the pan and saute for about 3 minutes. Add the minced garlic and cook for another 2 minutes
Add the tomato paste to the pan and mix with the butter, onion and garlic. Allow the tomato paste to toast in the pan for about 3 minutes. You want to be able to smell tomato cooking.
Carefully pour the vodka into the pan and mix in with the tomato paste. Let this cook for about 2 minutes stirring the whole time.
Pour heavy cream and parmesan cheese into the pan. Stir constantly until a smooth creamy sauce remains. Pour the cooked rigatoni noodles and 1/2 cup reserved pasta water into the pan. Toss to combine everything.
Allow the noodles to cook in the sauce for a couple minutes to ensure that each noodle is nicely coated. Serve with more freshly grated parmesan cheese