1. Preheat the oven to 375°F.

2. Bring a large pot of salted water to a boil and cook the jumbo pasta shells until al dente, about 9 to 10 minutes. Drain, rinse with cool water, and set aside.

3. Heat the olive oil in a skillet over medium heat. Add the minced garlic and cook for 30 seconds until fragrant.

4. Add the spinach and cook until wilted. If using frozen spinach, make sure it is thawed and fully squeezed dry before adding. Let the mixture cool slightly.

5. In a large bowl, combine the ricotta cheese, 3/4 cup of the mozzarella, Parmesan, egg, spinach mixture, salt, black pepper, and nutmeg. Stir until smooth and evenly combined.

6. Spread about 1 to 1 1/2 cups of marinara sauce across the bottom of a 9×13-inch baking dish.

7. Fill each shell with the ricotta and spinach mixture using a spoon or small scoop.

8. Arrange the filled shells in the baking dish in a single layer.

9. Spoon the remaining marinara sauce over the shells and sprinkle with the remaining mozzarella cheese.

10. Cover with foil and bake for 25 minutes.

11. Remove the foil and bake for another 10 to 15 minutes until the cheese is melted and lightly golden.

12. Let the shells rest for 5 to 10 minutes, then garnish with parsley or basil and serve warm.