01 -
Preheat oven to 375°F. Cook jumbo pasta shells in salted water following package directions, stirring occasionally to prevent sticking. Drain and submerge in cold water to halt cooking and keep shells separated.
02 -
Heat olive oil in a deep pan over medium-high heat. Sauté chopped onion until softened and golden, about 3 to 5 minutes. Add minced garlic, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and dried oregano; cook for 1 minute until fragrant. Stir in marinara sauce, bring to a boil, then reduce to simmer for 2 minutes. Transfer sauce to the bottom of a 9x13-inch casserole dish.
03 -
In a large bowl, combine ricotta, 2 cups mozzarella, parmesan, egg, chopped parsley, remaining 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Stir until evenly blended.
04 -
Using approximately half an ice cream scoop, fill each pasta shell with cheese mixture without overstuffing. Arrange filled shells in a single layer over the marinara sauce in the casserole dish. Sprinkle the remaining 1 cup of mozzarella evenly over the top.
05 -
Cover the casserole with foil and bake for 30 minutes until sauce bubbles at the edges. Remove foil and broil for 2 to 4 minutes to lightly brown the cheese. Remove from oven and garnish with fresh parsley before serving.