Cook the pasta: Bring a large pot of salted water to a boil. Cook rigatoni until al dente. Reserve 1 cup of pasta water, then drain.
Brown the sausage: Heat olive oil in a large skillet over medium heat. Add the Italian sausage, breaking it into small pieces. Cook until browned and crispy, about 5-7 minutes. Remove and set aside.
Sauté aromatics: In the same pan, add diced onion and cook until soft (about 3 minutes). Add garlic and cook for another 30 seconds. Tomato paste & vodka: Stir in tomato paste and cook for 2 minutes until deep red. Pour in the vodka, scraping up any bits from the pan. Let it cook for 2 minutes. Make it creamy & spicy: Lower the heat and add heavy cream and red pepper flakes. Stir until combined.
Combine everything: Return the cooked sausage to the pan, then add the rigatoni and toss to coat. If needed, add reserved pasta water a little at a time to loosen the sauce.
Finish with cheese: Stir in Parmesan, season with salt and black pepper, and toss until creamy.
Serve: Garnish with fresh basil or parsley, and extra Parmesan.
