In a large skillet, heat a drizzle of olive oil over medium heat. Add the ground Italian sausage and cook for about 5–7 minutes, breaking it up with a spatula until it’s browned and fully cooked. Remove from the skillet and let it drain on paper towels.

In a separate pot, bring salted water to a boil and add the rigatoni. Cook according to package directions until al dente, about 10–12 minutes. Drain the pasta and set aside, reserving a cup of the pasta water.

Using the same skillet, add a tablespoon of butter and another drizzle of olive oil over medium-low heat. Toss in the chopped red onion and sauté for about 3–4 minutes until softened. Add minced garlic and cook for another minute until fragrant.

Stir in the tomato paste and a pinch of salt, allowing it to meld with the onions for about 2 minutes. Gradually whisk in the heavy cream until smoothly combined, followed by mixing in freshly grated parmesan and desired red pepper flakes. Simmer for 2–3 minutes until slightly thickened.

Return the cooked sausage and drained rigatoni to the skillet with the sauce. Stir everything together for about 2 minutes, ensuring pasta is coated in the creamy sauce. If too thick, add a splash of reserved pasta water.

Remove from heat, transfer to plates or a serving bowl, and finish with a sprinkle of parsley and dusting of extra parmesan. Serve immediately.