In a pot, bring water to boil. Add rigatoni pasta and cook until al dante, according to package instructions. Halfway through, reserve 1 cup of pasta water and set aside for later. When pasta is done cooking, drain and set aside.
In a skillet, melt butter under medium high heat and add diced onions. Cook for 1-2 minutes or until onions are slightly translucent, then add minced garlic, Cook for 30 seconds or until garlic is fragrant.
Add tomato puree, tomato paste and red pepper flakes. Stir to combine and bring to boil.
Make sure heat is still on medium high. Add vodka and it should evaporate quickly. Stir to combine and cook for 4-5 minutes.
Add heavy cream and 1/2 cup of the reserved pasta water. Stir and bring to a boil. Lower to medium heat and let it cook for 5 minutes, stirring frequently. Add more pasta water to dilute sauce if needed.
Switch off heat and add rigatoni pasta to sauce. Toss to combine.
Sprinkle with parmesan cheese. Serve and enjoy!