Instructions

• Preheat oven to 375°F.
• Cook the 20 jumbo pasta shells according to package instructions. Do not add additional salt to the pasta water—the recipe's 1 tsp salt is reserved for the sauce and filling. Stir several times while cooking to prevent sticking. Drain the shells and rinse under cold water to stop the cooking and keep them from sticking; lay them out in a single layer on a sheet pan or plate and set aside.
• Make the sauce: Heat a large nonstick or heavy-bottomed skillet over medium-high heat. Add the 1/2 medium chopped onion and sauté, stirring frequently, until softened and golden, about 3–5 minutes. Add the 3 minced garlic cloves, 1/2 tsp of the recipe salt (from the 1 tsp), 1/4 tsp black pepper (from the 1/2 tsp), and 1/4 tsp dried oregano; sauté, stirring constantly, for about 1 minute until the garlic is fragrant. Add the 3 cups marinara sauce, bring to a simmer, and cook 2 minutes. Pour the sauce evenly into the bottom of a 9×13-inch casserole dish.
• Make the cheese filling: In a large bowl, combine 15 oz ricotta cheese, 2 cups of the shredded mozzarella (reserve 1 cup for the top), 1/3 cup Parmesan cheese, 1 large egg, 1/4 cup chopped parsley, the remaining 1/2 tsp salt, and the remaining 1/4 tsp black pepper. Stir until the mixture is well combined.
• Stuff the shells: Using about a 1/2 ice cream scoop or a spoon, fill each cooked shell with the cheese mixture (do not overstuff). Place the 20 filled shells in a single layer over the marinara in the casserole dish.
• Sprinkle the reserved 1 cup shredded mozzarella evenly over the filled shells. Cover the dish tightly with foil.
• Bake covered at 375°F for 30 minutes, until the sauce is bubbling at the edges. Remove the foil and broil for 2–4 minutes, watching closely, until the cheese is lightly browned.
• Remove from the oven, garnish with additional parsley as desired, and serve.