Get the Pasta Ready: Bring a large pot of salted water to a rolling boil. Cook the jumbo pasta shells according to package instructions until just al dente. Drain the pasta and allow it to cool slightly.
Cook the Meat: In a skillet over medium heat, cook the ground beef, breaking it up as it browns. Season with salt and pepper. Once fully cooked, drain any excess grease and let cool.
Make the Filling: In a large bowl, combine the cooked ground beef, ricotta cheese, 1 cup of mozzarella, Parmesan, egg, parsley, minced garlic, and Italian seasoning. Mix until everything is well incorporated.
Fill the Shells: Preheat your oven to 375°F (190°C). Spread a layer of marinara sauce on the bottom of a 9×13-inch baking dish. Stuff each shell with about 1-2 tablespoons of the meat mixture and arrange it in the baking dish.
Add Sauce and Cheese: Pour the remaining marinara sauce over the Stuffed Shells with Meat, covering them completely. Sprinkle the remaining mozzarella cheese evenly on top.
Bake: Cover the dish with foil and bake for 30 minutes, then uncover and bake for another 10 minutes, or until the cheese is melted, bubbly, and golden.
Garnish and Serve: Let the Stuffed Shells with Meat cool for a few minutes, then garnish with fresh basil if desired. Serve warm.