Preheat your oven to 375 degrees. 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 egg, ricotta cheese, 2 cups of mozzarella cheese, 1/4 cup Parmesan cheese, garlic, parsley, basil, salt, and black pepper. Add the mixture to a large ziplock bag and then cut off the tip. Use this to pipe the cheese 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.
Cover and bake for 30 minutes. Uncover and bake for an additional 5 minutes. Serve, and enjoy.