How to Make It
Preheat oven to 400°F. In a large pot of boiling, salted water, cook shells 2 minutes less than time specified on package, about 9 minutes. Drain and rinse with cool water.
In a large bowl, mix ricotta, spinach, Parmesan, pecorino, garlic, parsley and 2 cups mozzarella. Season with salt and pepper. Stir in egg.
Spread half of tomato sauce in a 9-by-13-inch dish. Fill each shell with 1 heaping Tbsp. ricotta mixture and place open side up in dish. Spoon remaining sauce over shells; sprinkle with remaining mozzarella. Cover with foil and bake 30 minutes. Remove foil and bake 20 to 30 minutes, until bubbling. Let stand 5 minutes; serve.