Bring a large pot of water to a rolling boil and add the salt. Cook the manicotti shells for 2 minutes less than the package directions indicate. Drain carefully and lay them in a single layer on a sheet pan drizzled with olive oil, tossing gently to coat each shell.

Heat a large skillet over medium-high heat and add the ground beef and Italian sausage. Break the meat into small pieces as it cooks until no pink remains, about 8 to 10 minutes. Drain any excess fat.

Add the minced garlic to the cooked meat and stir for about 30 seconds until fragrant. Stir in the Italian seasoning, salt, and pepper, then remove the skillet from heat to cool slightly.

In a large bowl, combine the ricotta cheese, 1/2 cup Parmesan, beaten egg, and parsley. Add the cooled meat mixture and stir until everything is well combined. Taste and adjust seasoning as needed.

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

Using a small spoon or piping bag, carefully fill each manicotti shell with the meat mixture, working from both ends to ensure the filling reaches the center. Arrange the filled shells in a single layer over the sauce in the baking dish.

Pour the remaining marinara sauce over the filled manicotti, making sure each shell gets covered. Sprinkle the shredded mozzarella and 1/4 cup grated Parmesan evenly over the top. Cover the dish tightly with aluminum foil.

Bake covered for 25 minutes. Remove the foil and bake for an additional 15 to 20 minutes until the cheese turns golden and bubbly.

Let the dish rest for 5 minutes before serving. Garnish with fresh basil.