Start by preheating your oven to 375°F (190°C). This will ensure it’s hot and ready for the pasta shells once assembled.
Bring a large pot of salted water to a boil and add the jumbo pasta shells. Cook them according to the package instructions until they are al dente, usually about 9-11 minutes. Once done, drain the shells and set them aside to cool slightly.
In a spacious mixing bowl, combine the chopped spinach with the ricotta cheese, 1/2 cup of the mozzarella cheese, grated Parmesan cheese, and the beaten egg. Add garlic powder, onion powder, salt, and black pepper. Stir everything together vigorously until the mixture is smooth and evenly blended.
Take each pasta shell and carefully fill it with a generous amount of the spinach and ricotta mixture using a spoon. Place the stuffed shells seam-side up in a greased 9x13-inch baking dish. Make sure they are arranged side by side without overlapping.
Pour 1 cup of marinara sauce evenly over the stuffed shells, making sure each shell is coated. Sprinkle the remaining 1/2 cup of mozzarella cheese generously over the top for that lovely melty finish.
To ensure even cooking and prevent the cheese from burning, cover the baking dish tightly with aluminum foil and bake in the preheated oven for 25 minutes.
After 25 minutes, remove the foil carefully (watch out for steam!) and continue to bake for an additional 10 minutes, or until the cheese is nicely bubbly and elegantly golden brown.
Once baked to perfection, remove the dish from the oven and allow the shells to cool for a few minutes before serving. Garnish with fresh basil leaves for an aromatic touch if desired.
Notes
Serve directly in the baking dish, garnished with fresh basil and extra marinara sauce.