Begin by bringing a large pot of generously salted water to a boil. Add the pasta and cook until al dente, following the instructions on the package. Before draining, reserve 1 cup of the pasta cooking water. Drain the pasta and return it to the pot, keeping it covered to stay warm.
In a high-speed blender, combine the marinara sauce, cottage cheese, parmesan cheese, melted butter, red pepper flakes, and the reserved pasta water. Blend until the mixture is smooth and creamy, which should take about 1-2 minutes.
Pour the blended sauce over the cooked pasta. Toss well until the pasta is thoroughly coated and the dish is heated through. Serve immediately, garnishing with additional red pepper flakes and chopped parsley if desired.