Creating Spinach and Ricotta Stuffed Shells is simple when you follow these steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Cook Pasta: In a large pot of boiling salted water, cook the pasta shells according to package instructions until al dente. Drain and set aside.
3. Prepare Filling: In a large bowl, combine ricotta cheese, chopped spinach, 1/2 cup mozzarella cheese, grated Parmesan cheese, egg, garlic powder, salt, and black pepper. Mix until well combined.
4. Stuff Shells: Carefully fill each cooked pasta shell with the ricotta-spinach mixture, using a spoon or piping bag for ease.
5. Prepare Baking Dish: Spread 1 cup of marinara sauce evenly on the bottom of a 9×13 inch baking dish.
6. Place Shells: Arrange the stuffed shells in the baking dish in a single layer, open side up.
7. Add Sauce: Pour the remaining marinara sauce over the stuffed shells, ensuring they are well covered.
8. Top with Cheese: Sprinkle the remaining mozzarella cheese over the top of the shells.
9. Bake: Cover the baking dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
10. Garnish and Serve: Once baked, remove from the oven and let cool for a few minutes. Garnish with fresh basil if desired.

Following these steps will guide you to create delicious Spinach and Ricotta Stuffed Shells that everyone will love.