FIRST STEP: COOK THE PASTA SHELLS

1. Boil the Pasta: Bring a large pot of salted water to a boil. Add the jumbo pasta shells and cook according to the package instructions, about 8-10 minutes, until they are al dente.
2. Drain and Cool: Once cooked, drain the shells and rinse them under cold water to stop the cooking process. Set the shells aside to cool completely.

SECOND STEP: PREPARE THE SPINACH AND RICOTTA FILLING

1. Sauté the Onion and Garlic: In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the chopped onion and sauté for about 5 minutes, or until the onion becomes soft and translucent. Add the minced garlic and cook for an additional 1 minute until fragrant.
2. Cook the Spinach: Add the thawed spinach (or fresh spinach if using) to the skillet. Stir the spinach and cook for 3-4 minutes, until the spinach is wilted and the liquid evaporates. Remove the skillet from the heat and allow the mixture to cool for a few minutes.
3. Make the Filling: In a large mixing bowl, combine the ricotta cheese, shredded mozzarella, grated Parmesan cheese, egg, sautéed spinach mixture, salt, and pepper. Stir everything together until fully incorporated. The filling should be thick and creamy.

THIRD STEP: MAKE THE MARINARA SAUCE

1. Heat Olive Oil: In a medium saucepan, heat 1 tablespoon of olive oil over medium heat. Add the minced garlic and sauté for 1 minute until fragrant.
2. Add the Sauce and Herbs: Pour in the marinara sauce and add the dried basil and oregano. Stir to combine, then bring the sauce to a simmer. Season with salt and pepper to taste. Let the sauce simmer for about 10-15 minutes to allow the flavors to meld.

FOURTH STEP: STUFF THE PASTA SHELLS

1. Preheat the Oven: While the sauce is simmering, preheat your oven to 375°F (190°C).
2. Fill the Shells: Take each cooled pasta shell and carefully stuff it with the spinach and ricotta filling. You can use a spoon or your hands to pack the filling inside. Be generous with the filling for a satisfying bite.
3. Arrange in a Baking Dish: Pour a thin layer of marinara sauce on the bottom of a 9×13-inch baking dish. Place each stuffed shell in the dish, open side up, until the dish is full. Pour the remaining marinara sauce over the stuffed shells, covering them completely.

FIFTH STEP: BAKE THE STUFFED SHELLS

1. Top with Cheese: Sprinkle the shredded mozzarella cheese evenly over the top of the stuffed shells, covering them with a layer of cheese.
2. Bake: Cover the baking dish with aluminum foil and bake the stuffed shells in the preheated oven for 25-30 minutes, until the cheese is melted and bubbly. Remove the foil in the last 5-10 minutes of baking to allow the cheese to brown slightly.
3. Cool and Serve: Once baked, remove the dish from the oven and let it cool for 10 minutes before serving. Garnish with fresh basil leaves for a burst of color and freshness.