Boil the Pasta: Bring a large pot of salted water to a rolling boil. Add the jumbo pasta shells and cook them until al dente, about 8-10 minutes. Drain and spread them on a baking sheet to cool, preventing them from sticking together.

Sauté the Spinach: In a skillet over medium heat, pour in the olive oil. Add the minced garlic and sauté until fragrant, about 1 minute. Toss in the fresh spinach and cook until wilted, about 2-3 minutes. Remove from heat, chop roughly, and set aside to cool.

Mix the Filling: In a large mixing bowl, combine the ricotta, chopped spinach, mozzarella, parmesan, egg, salt, and pepper. Stir until everything is fully incorporated and the mixture is creamy.

Fill the Shells: Using a spoon or piping bag, fill each pasta shell with the ricotta-spinach mixture. In a baking dish, spread 1 cup of marinara sauce on the bottom, then nestle the filled shells in a single layer.

Sauce It Up: Pour the remaining marinara sauce over the stuffed shells until they are covered. Sprinkle extra mozzarella and parmesan cheese on top.

Bake the Dish: Cover with foil and bake at 375°F (190°C) for 20 minutes, then uncover and bake for an additional 10-15 minutes until the cheese is bubbly and golden.

Rest and Serve: Let the pasta sit for 5-10 minutes after removing from the oven. Garnish with fresh parsley and additional cheese before serving.