Bring a large pot of salted water to a boil and cook pasta according to package directions until al dente, about 8-10 minutes. Before draining, reserve ½ cup of the starchy pasta water.

While the pasta cooks, heat 2 tablespoons olive oil in a large skillet over medium heat. Add the diced onion and cook for 4-5 minutes until translucent and softened. Add minced garlic and sauté for 1 minute until fragrant.

Transfer the sautéed onion and garlic to a blender along with the drained roasted red peppers and cottage cheese. Blend on high for 30-45 seconds until completely smooth and creamy.

Pour the blended sauce back into the same skillet over medium-low heat. Season with salt, black pepper, and chili flakes if using. Let it simmer gently for 5 minutes, stirring occasionally. If the sauce seems too thick, add reserved pasta water 2 tablespoons at a time until you reach desired consistency.

Add the drained pasta directly to the sauce and toss until every piece is evenly coated. Sprinkle with freshly grated Parmesan and chopped parsley, toss once more, and serve immediately while hot.