In a large bowl, combine sausage and cottage cheese. Stuff into uncooked manicotti shells. Place in a greased 13×9-in. baking dish. Top with marinara sauce.
Cover and bake at 350° for 55-60 minutes or until a thermometer inserted into the center of a shell reads 160°.
Uncover; sprinkle with mozzarella cheese. Bake 8-10 minutes longer or until cheese is melted. Let stand for 5 minutes before serving. Freeze option: Transfer individual portions of cooled manicotti to freezer containers; freeze. To use, partially thaw in refrigerator overnight. Transfer to a microwave-safe dish and microwave on high, stirring occasionally and adding a little spaghetti sauce if necessary.