Preheat your oven to 400°F (200°C).

In a large pot, bring salted water to a boil and add the jumbo pasta shells. Cook until al dente, approximately 10-12 minutes.

Combine the ricotta cheese, grated parmesan, thawed spinach, egg, salt, and pepper in a large mixing bowl. Mix until a creamy filling forms.

Using a piping bag, fill each shell with about 2 tablespoons of the ricotta mixture.

Spread half of the marinara sauce across the bottom of the casserole dish. Place filled shells in a single layer.

Pour the remaining marinara sauce over the shells and sprinkle shredded mozzarella on top.

Cover with foil and bake for 20-25 minutes or until the sauce is bubbling and cheese is melted.

Garnish with fresh basil and serve hot.