Bring a large pot of water to a rolling boil and add the salt. Cook the manicotti shells for 6 to 7 minutes, about 2 minutes less than the package directions, so they remain firm enough to handle.

Drain the shells carefully and lay them flat on a lightly oiled baking sheet to prevent sticking.

Heat a large skillet over medium-high heat and add the ground beef, breaking it apart with a wooden spoon. Cook for 6 to 8 minutes until no pink remains and the meat develops some browned bits.

Add the minced garlic during the last minute of cooking and stir constantly so it becomes fragrant without burning. Drain any excess fat, then transfer the meat to a large bowl and let it cool for 5 minutes.

Add the ricotta, 1 cup mozzarella, Parmesan, egg, parsley, oregano, salt, and pepper to the bowl with the cooled meat. Mix everything together with a spoon until thoroughly combined and the mixture looks uniform.

Preheat your oven to 375°F. Spread 1 cup of marinara sauce evenly across the bottom of your 9x13 inch baking dish.

Transfer the meat and cheese mixture to a piping bag or a large zip-top bag with one corner cut off. Gently squeeze the filling into each manicotti shell, working from one end until it feels full but not bursting.

Arrange the stuffed shells in a single layer over the sauce in the baking dish, placing them seam-side up if there's a split.

Pour the remaining 2 cups of marinara sauce over the stuffed shells, making sure each one gets covered. Use the back of a spoon to spread the sauce into any gaps.

Sprinkle the 1 1/2 cups of mozzarella and 1/4 cup of Parmesan evenly over the top.

Cover the baking dish tightly with aluminum foil and place it in the preheated oven. Bake for 30 minutes, then remove the foil and continue baking for another 15 minutes until the cheese turns golden brown and the sauce bubbles vigorously around the edges.

Remove the pan from the oven and let it rest for 10 minutes before serving. Garnish with fresh basil leaves if desired, and serve hot with extra Parmesan on the side.