Bring a large pot of salted water to a boil. Cook the rigatoni pasta according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta and set aside.

In a large skillet, heat olive oil over medium heat. Add diced onion and cook until translucent, about 3-4 minutes.

Add minced garlic and red pepper flakes to the skillet, cooking for about 1 minute until fragrant.

Stir in tomato paste and cook for 2 minutes, then pour in vodka. Allow the alcohol to evaporate, about 2 minutes.

Lower the heat and add heavy cream, stirring well. Cook for 5 minutes until the sauce thickens slightly.

Add the cooked rigatoni to the sauce, tossing to coat evenly. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached.

Stir in grated Parmesan cheese and season with salt to taste. Cook for an additional 2 minutes to meld the flavors.

Serve hot, garnished with extra Parmesan if desired.