Preheat oven to 375°F. Lightly spray a 9x13-inch baking dish with nonstick spray. Set aside.
Bring a pot of water on the stovetop to a boil. Cook the pasta shells to al dente. After cooking the pasta shells, drain and place them upside down on a baking sheet to dry.
12 ounces jumbo pasta shells
Make the filling. In a large bowl, combine the egg, ricotta cheese, 1 cup mozzarella cheese, ¼ cup parmesan cheese, sour cream, Italian seasoning, salt, and pepper. Mix well, then fold in the shredded chicken.
Stuff each shell with the filling and arrange them side by side, open side up, in the prepared baking dish.
Evenly spread the Alfredo sauce on top of the stuffed shells. Top with the remaining mozzarella and parmesan cheeses.
15 ounces Alfredo sauce
Cover with foil and bake for 25 minutes, then remove the foil and continue baking for another 10 minutes, until bubbly. For golden cheese, broil for 1-3 minutes.
Garnish with fresh parsley and serve.
Chopped fresh parsley