1. Preheat oven to 375ยฐF.
2. Bring a large pot of salted water to boil. Cook rotini according to package directions until just under al dente, about 12 minutes. Drain and set aside, reserving 1/2 cup pasta water.
3. Heat olive oil in a large oven-safe skillet over medium heat. Add onion and cook until beginning to brown, about 5 minutes. Add garlic and Italian sausage and cook until well browned, breaking it up with a wooden spoon as it cooks, about 5 minutes. Deglaze the pan with a little water if needed so that the onions and garlic donโt burn.
4. Meanwhile, combine marinara sauce and cottage cheese in a blender until smooth.
5. Remove skillet from heat. Add sauce and rotini to pan, stirring well to coat. Taste and season with salt and pepper as needed. Spread pasta and sauce evenly in skillet, then sprinkle with mozzarella and Parmesan cheese.
6. Bake until sauce is bubbling and cheese is melted, about 15 to 20 minutes. Sprinkle with chopped basil and serve immediately.