Preheat your oven to 375 degrees Fahrenheit. Spray a 9 by 13 inch baking dish with cooking spray.
Cook the shells according to package instructions. Make sure the water is at a full boil before you put in the uncooked shells. Add 1 teaspoon of kosher salt to the water and set a timer so that the pasta is drained just before it is al dente.
While the pasta is cooking, in a large bowl combine the cooked sausage, egg, ricotta cheese, 1 cup of mozzarella cheese, garlic, parsley, basil, salt, and black pepper. Spoon the mixture into the shells.
Pour 1 cup of sauce onto the prepared casserole dish to coat the bottom. Place the filled shells, seam side up, in the pan. Top with the remaining sauce, 1 cup of mozzarella cheese, and 1/4 cup of Parmesan. You may have some filling left over. We typically stuff the extra shells and cook them in a smaller casserole dish.
Cover and bake for 30 minutes. Uncover and bake for an additional 5 minutes. Serve, and enjoy.