Pre-heat oven to 350 degrees.
Cook pasta shells according to package instruction. Gently stir the shells as the cook to hep prevent them from sticking together. (TIP: Make a few extra shells in the event some tear or stick). When pasta is slightly uncooked, remove, drain, and lightly rinse.
In a medium bowl, mix together beef, sausage, egg, breadcrumbs, milk, seasonings, and 2 tbsp of Parmesan cheese. Roll mixture into 1 ½ inch meatballs, you should make 25 meatballs.
Place ⅓ cup of sauce in the bottom of a 9x13 inch baking dish. Spread sauce into an even layer. Place a meatball securely in each shell. Arrange shells into 5 rows of 5 in the baking dish.
Top shells with remaining sauce. Top with mozzarella and Parmesan cheese. Top with parsley.
Bake uncovered for 40 minutes. Serve immediately.