Step 1: Cook the Pasta Shells

• Boil the shells: Bring a large pot of salted water to a boil. Add the jumbo pasta shells and cook according to the package instructions until al dente. Drain the shells and drizzle with olive oil to prevent sticking. Set aside.

Step 2: Prepare the Filling

• Mix the cheeses: In a large bowl, combine the ricotta cheese, 1 cup of the mozzarella, Parmesan cheese, and the thawed, squeezed spinach.
• Add seasonings: Stir in the beaten egg, Italian seasoning, minced garlic, salt, and pepper. Mix until the filling is well combined.

Step 3: Assemble the Dish

• Preheat the oven: Set the oven to 375°F (190°C).
• Fill the shells: Spoon the ricotta mixture into the cooked pasta shells, about 2 tablespoons per shell, and set them aside.
• Prepare the baking dish: In a large baking dish, spread 1-2 cups of marinara sauce over the bottom.
• Arrange the shells: Place the filled pasta shells on top of the sauce, open side up. Spoon the remaining marinara sauce over the shells, making sure they are well-covered.

Step 4: Bake the Stuffed Shells

• Add more cheese: Sprinkle the remaining ½ cup of mozzarella cheese over the top of the shells.
• Bake: Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
• Broil for a golden top (optional): For a golden, crispy top, broil the dish for the last 2-3 minutes, watching closely to avoid burning.

Step 5: Serve

• Garnish and serve: Remove the stuffed shells from the oven and let them rest for a few minutes before serving. Garnish with fresh basil, if desired, and serve warm.