Bring a large pot of salted water to a rolling boil over high heat. Add the rigatoni and cook according to package instructions until al dente, usually about 10-12 minutes. Reserve ½ cup of the pasta water, then drain the rest in a colander. Set the rigatoni aside while you prepare the sauce.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until softened and translucent. Add minced garlic and cook for an additional 30 seconds, stirring frequently until fragrant but not browned.

Stir in 2 tablespoons of tomato paste, followed by the crushed tomatoes, Italian seasoning, salt, and optional red pepper flakes. Mix well and bring the sauce to a simmer. Let it cook for about 10 minutes, stirring occasionally.

Carefully transfer the marinara sauce to a blender. Add 1 cup of cottage cheese and ½ cup of grated Parmesan cheese. Blend until smooth and creamy.

Return the blended sauce to the skillet over low heat, and add the drained rigatoni. Toss the pasta gently in the sauce until thoroughly coated, approximately 2-3 minutes.

Taste the rigatoni and adjust the seasoning with more salt or pepper if needed. Serve immediately in warm bowls, garnished with additional grated Parmesan and fresh parsley.