Heat a pot of salted water to a boil, add pasta shells and cook until just tender.
While the pasta is cooking, to a large mixing bowl, add the crab meat, shrimp, egg, ½ of the Mozzarella cheese, ½ of the Parmesan cheese, and all of the cottage cheese. Stir together until combined.
When the pasta is ready, drain and run under cold water to stop the cooking process.
Preheat your oven to 180° C (350° F). Spray a 9x13 glass baking dish with butter flavored cooking spray.
Stuff a shell generously with the seafood mixture and place in the prepared baking dish. Repeat the remaining shells.
In a medium sauce pan on medium heat, melt the butter. Add the onion and saute until the onion is soft and translucent.
Whisk in the flour, then slowly whisk in the half and half. Simmer until sauce is just thickened. Taste and season with salt and pepper as desired.
Pour the sauce over the stuffed shells.
Sprinkle the remaining Mozzarella and Parmesan cheeses over the shells. Sprinkle the top with the Old Bay Seasoning.
Bake uncovered for 30 minutes.
Serve with sides of your choice, enjoy.