Start by preheating your oven to 375°F (190°C) to prepare for baking.
In a large pot, bring salted water to a boil and cook the jumbo pasta shells according to the package instructions until they are al dente (typically about 8-10 minutes). Once cooked, drain the shells and set them aside in a colander to cool slightly.
In a mixing bowl, combine the ricotta cheese, finely chopped spinach, half of the shredded mozzarella cheese, grated Parmesan cheese, the beaten egg, freshly chopped basil, garlic powder, and a pinch of salt and pepper. Stir everything together until the mixture is smooth and evenly combined.
Carefully take each pasta shell and fill it with a generous spoonful of the ricotta and spinach mixture. Place the stuffed shells seam-side up in a greased baking dish, ensuring they are snug but not overcrowded.
Spread half of the marinara sauce evenly over the stuffed shells, making sure to cover them well for flavor and moisture.
For an extra cheesy delight, sprinkle the remaining shredded mozzarella cheese over the top of the shells.
Pour the rest of the marinara sauce over the shells, ensuring that every shell is well coated in sauce for that perfect bake.
Cover the baking dish with aluminum foil to trap moisture, and bake in the preheated oven for 25 minutes. After that time, remove the foil and continue to bake for an additional 10-15 minutes, or until the cheese on top is bubbling and beautifully golden brown.
Once done, remove the baking dish from the oven and allow the shells to cool for a few minutes before serving.
Notes
Serve with warm garlic bread and a simple green salad.