Prep Pasta: Bring a large pot of salted water to a boil. Cook the jumbo pasta shells according to package instructions until al dente, about 9-11 minutes. Drain and set aside to cool.

Sauté Spinach: In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add 2 minced cloves of garlic and sauté for about 30 seconds. Toss in 4 cups of fresh spinach, cooking until wilted, about 2-3 minutes. Remove and allow to cool slightly.

Combine Filling: In a mixing bowl, combine sautéed spinach with 15 ounces ricotta cheese, 1 cup mozzarella, and ½ cup parmesan. Add 1 beaten egg, chopped basil, salt, and pepper. Stir until smooth.

Stuff Shells: Fill each cooled pasta shell with the cheesy spinach mixture. Set the stuffed shells aside.

Arrange: Preheat oven to 375°F (190°C). Spread 1 cup marinara sauce at the bottom of a 9x13 inch baking dish. Place stuffed shells upright and pour remaining marinara sauce over the top.

Bake: Cover baking dish with foil and bake for 25 minutes. Remove foil and bake for an additional 10-15 minutes until golden and bubbly.

Serve: Let the dish cool for 5-10 minutes before serving warm topped with fresh basil or grated parmesan.