Bring a large pot of salted water to a boil. Add the jumbo shells and cook according to package instructions until al dente. Drain and set aside to cool slightly so they’re easier to handle.

In a large skillet, heat olive oil over medium heat. Add the chopped onion and cook for 3–4 minutes until soft. Stir in garlic and cook for another minute.

Add the ground beef, breaking it apart with a spoon. Cook until browned and fully cooked. Season with salt, pepper, and Italian seasoning. Remove from heat and let it cool slightly.

In a mixing bowl, combine ricotta cheese, 1 cup mozzarella, Parmesan cheese, egg, and parsley. Mix until smooth and well combined.

Add the cooked ground beef mixture to the cheese mixture and stir until everything is evenly combined.

Preheat your oven to 180°C (350°F). Spread a thin layer of marinara sauce on the bottom of your baking dish.

Carefully stuff each shell with the beef and cheese mixture and place them in the dish. Once all shells are filled, pour the remaining sauce over the top.

Sprinkle the remaining mozzarella cheese evenly over everything.

Cover the dish with foil and bake for 25 minutes. Remove the foil and bake for another 10–15 minutes until the cheese is melted and bubbly.

Let the dish rest for 5–10 minutes before serving. Garnish with extra parsley if desired.