Begin by boiling a large pot of salted water. Add the jumbo pasta shells and cook according to package instructions for about 8–10 minutes until al dente. Once cooked, drain the shells and lay them out on a clean kitchen towel to cool slightly.

In a mixing bowl, combine the ricotta cheese, ½ cup of shredded mozzarella, grated Parmesan cheese, and a beaten egg. Stir thoroughly until the mixture is smooth and creamy.

In a skillet, heat 1 tablespoon of olive oil over medium heat. Add minced garlic and sauté for 30 seconds until fragrant, then toss in the fresh spinach. Cook the spinach for about 2–3 minutes until it wilts down. Remove from heat and let it cool slightly before mixing it into the cheese filling.

Once the spinach has cooled, fold it into the ricotta mixture. Season the filling with Italian seasoning, salt, and black pepper to your liking.

Preheat your oven to 375°F (190°C). Spread 1 cup of marinara sauce evenly across the bottom of a 9"x13" baking dish.

Carefully take each cooked pasta shell and fill it with approximately 2 tablespoons of the spinach and ricotta filling. Arrange the stuffed shells open-side up in the prepared baking dish, then spoon the remaining marinara sauce over them.

Cover the baking dish with aluminum foil and bake for 20 minutes. Afterward, remove the foil and sprinkle the remaining shredded mozzarella on top. Bake uncovered for an additional 10 minutes, until the cheese is bubbly and golden brown.

Once done, remove from the oven and let them rest for about 5 minutes. Garnish with fresh basil before serving.