Preheat an oven to 350 degrees F (175 degrees C). Grease a 2.5 quart baking dish.
Bring a large pot of lightly salted water to a boil. Place pasta in the pot, cook for 8 to 10 minutes, until tender, and drain.
Cook and stir the Italian sausage in a large skillet over medium heat until browned, about 8 to 10 minutes. Drain the fat from the meat, pour the cooked pasta and spaghetti sauce into the skillet, and stir well to combine. Bring the mixture to a boil.
Pour half of the hot pasta-sausage mixture into the prepared baking dish, spread with the cottage cheese in an even layer, and sprinkle with half the mozzarella cheese. Spread the remaining pasta mixture over the cheese, and top with the remaining mozzarella cheese.
Cover and bake in the preheated oven for about 25 minutes, until the casserole is hot and the cheese is melted and bubbling. Let it stand 5 minutes to firm up before serving.