Follow these simple steps to create your stuffed shells:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Cook the Shells: In a large pot of boiling salted water, cook the pasta shells according to package directions until al dente. Drain and set aside.
3. Mix the Filling: In a large bowl, combine the ricotta cheese, shredded mozzarella cheese, Parmesan cheese, egg, parsley, basil, garlic powder, salt, and pepper. Mix until well combined.
4. Fill the Shells: Using a spoon, carefully fill each cooked pasta shell with the cheese mixture. Aim for about 1-2 tablespoons of filling per shell.
5. Prepare the Baking Dish: Spread a thin layer of marinara sauce on the bottom of a 9×13-inch baking dish.
6. Arrange the Shells: Place the filled shells in the baking dish, seam side up, in a single layer.
7. Top with Sauce: Pour the remaining marinara sauce over the stuffed shells, ensuring they are well covered.
8. Add Cheese: Sprinkle additional mozzarella cheese on top if desired.
9. Cover and Bake: Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
10. Uncover and Continue Baking: After 20 minutes, remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and slightly golden.
11. Cool and Serve: Remove from the oven and allow to cool for a few minutes before serving.

By following these steps, you’ll create incredible stuffed shells that are sure to impress!