Heat olive oil in a large pot or Dutch oven over medium heat. Add diced onion and cook for 7 to 8 minutes, stirring occasionally, until softened and translucent.

Add minced garlic and Italian sausage with casings removed. Break sausage into small pieces with a wooden spoon and cook for 7 to 8 minutes until browned and cooked through with no pink remaining.

Bring a separate large pot of heavily salted water to a boil over high heat. Cook rigatoni until just al dente, 9 to 11 minutes. Reserve 1 cup of pasta water before draining.

Add canned tomatoes to the sausage mixture, crushing whole tomatoes by hand as you add them. Stir in basil, oregano, chili flakes, salt, and pepper. Bring to a boil, then reduce heat and simmer for 5 to 7 minutes.

Stir in heavy cream and 1 cup of Parmesan cheese. Reduce heat to medium-low and do not return to a full boil. Simmer gently for 5 to 7 minutes until the sauce thickens and turns deep orange-pink. Taste and adjust seasoning.

Drain rigatoni and add it to the sauce. Toss well to coat. If the sauce is too thick, stir in a splash of reserved pasta water to loosen it. Plate and top with remaining 1/2 cup Parmesan and fresh basil.