Instructions

• Preheat oven to 375°F and place the oven rack in the top third position.
• Bring a large pot of salted water to a boil. Add the 24 uncooked jumbo shells and cook for 1 minute less than the package directions specify. Drain the shells in a colander and let them sit until needed.
• While the shells cook (or before assembling), make sure the 16 ounces frozen spinach is fully thawed. Squeeze out as much liquid as possible (use your hands, a clean kitchen towel, or paper towels) and transfer the drained spinach to a large mixing bowl.
• Add 15 ounces ricotta cheese, 1 cup freshly grated Parmesan cheese, 1 egg, 1/2 teaspoon salt, pepper to taste, 1/2 teaspoon Italian seasoning, and 1/2 teaspoon garlic powder to the bowl with the spinach. Stir until evenly combined.
• Pour the entire (24-ounce) jar of marinara sauce into the bottom of a 9x13-inch casserole dish and spread it into an even layer.
• Using a small spoon, fill each cooked shell with the spinach–ricotta mixture. Place each filled shell, open side up, into the casserole dish on top of the marinara, arranging them in a single layer.
• Sprinkle 2 cups shredded mozzarella cheese evenly over the stuffed shells. Cover the casserole dish tightly with aluminum foil.
• Bake covered at 375°F for 30 minutes.
• Remove the foil and broil on high for 2–4 minutes, watching closely, until the mozzarella is melted and lightly browned. (Keep the oven rack in the top third position while broiling.)
• Remove from the oven and let the dish sit briefly. Serve immediately, garnished with fresh basil and/or chopped parsley if desired, and add extra salt and pepper to taste.