Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells according to the package instructions until al dente, then drain and set aside.
In a large bowl, combine ricotta cheese, 1 cup of mozzarella cheese, parmesan cheese, egg, salt, pepper, and parsley.
Spread 1 cup of marinara sauce across the bottom of a 9x13 inch baking dish.
Fill each cooked shell with the ricotta mixture and place in the baking dish, seam side up.
Pour the remaining marinara sauce over the stuffed shells and sprinkle with additional mozzarella cheese.
Cover the dish with foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 5-10 minutes, or until the cheese is melted and bubbly.
Garnish with additional parsley before serving, if desired.