Cook the pasta shells according to package instructions until al dente. Drain and set aside to cool.
In a mixing bowl, combine the ricotta cheese, chopped spinach, half of the mozzarella cheese, Parmesan cheese, beaten egg, fresh basil, garlic powder, salt, and pepper. Mix until well combined.
Carefully stuff each shell with a generous spoonful of the ricotta-spinach mixture and place them in a baking dish.
Spread half of the marinara sauce evenly over the stuffed shells.
Sprinkle the remaining mozzarella cheese on top of the shells for extra cheesiness.
Pour the remaining marinara sauce over the top, ensuring all shells are coated.
Cover the baking dish with foil and bake for 25 minutes. Then remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden brown.
Allow to cool for a few minutes before serving.
Notes
Serve on a large platter with extra marinara sauce and fresh basil for garnish. Garlic bread pairs well with this dish.