Boil 8 cups of water in a large pan over medium -high heat.
Gently pour the stuffed shells into the boiling water and boil for 9 minutes, then drain and set aside. (You'll need about 22-24 shells, but I boil the whole 12 ounces so I have extra in case some shells break.)
In a large bowl, combine the beef, pork, egg, cheese, bread crumbs, garlic, parsley and basil. Mix well.
Preheat the oven to 350 degrees. Spread about 3/4 cup sauce into the bottom of a 9x13 baking pan.
Using an ice cream scoop (or your hands), scoop the meat mixture and gently stuff it into the shells. Place the shells meat side up into the prepared pan, side by side to fill the pan.
Once the shells are all stuffed, pour the rest of the sauce overtop the shells and spread it around to cover all the shells.
Sprinkle the shredded mozzarella cheese over top.
Cut a piece of aluminum foil a little larger than your pan. Spray one side with cooking spray. Cover the baking pan (sprayed side down) and press to seal.
Bake covered for 40 minutes, then uncover and broil on low for 3-5 minutes to brown the cheese (watch this closely!).
After baking, sprinkle the top with fresh parsley and serve.
The calories shown are based on the recipe making 24 shells, with 1 serving being 3 shells. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate.