Preheat oven to 350 degrees. Grease a 13x9 inch baking dish. In a bowl combine the spaghetti sauce and the can of tomato sauce. In the bottom of the baking pan spread 1/2 cup of the sauce. Layer 1/2 of the cooked and drained shells on top. Spread 1/2 the sauce on top of shells and top with 1/2 the ricotta or cottage cheese. Sprinkle with 1/2 of the mozz. cheese and repeat the layer. Top with the parmesan cheese. Cover and bake for 35 minutes.
Can be creative and use spaghetti sauce with mushrooms or meat or vegetables if you like.