Bring a large pot of salted water to a boil.
Add rigatoni and cook until al dente according to package instructions.
Reserve about ½ cup pasta water, then drain the pasta.
Heat olive oil in a large skillet over medium heat.
Add diced onion and sauté for 5–6 minutes until softened.
Add minced garlic and cook for about 30 seconds until fragrant.
Stir in tomato paste and cook briefly to deepen flavor.
Add crushed tomatoes, Italian seasoning, red pepper flakes, salt, and black pepper.
Simmer the sauce for about 10 minutes until slightly thickened.
Transfer the sauce to a blender.
Add cottage cheese and Parmesan cheese.
Blend until completely smooth and creamy.
Pour the blended sauce back into the skillet.
Add the cooked rigatoni and toss until evenly coated.
Add a splash of reserved pasta water if needed to loosen the sauce.
Cook for another 1–2 minutes until heated through.
Garnish with fresh parsley and additional Parmesan before serving.