Start by bringing a large pot of salted water to a rolling boil. Add the pasta shells and cook until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet over medium-high heat, add the ground beef and cook for 5-7 minutes until browned, breaking it apart. Drain excess grease.

In a mixing bowl, combine the cooked pasta, browned beef, and tomato soup. Fold in half of the cheddar cheese until well-coated.

Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish. Pour the pasta mixture into the dish and spread evenly. Sprinkle the remaining cheddar cheese and all the mozzarella cheese on top.

Bake for 20-25 minutes until the cheese is melted and bubbly. Optionally broil for 2-3 minutes for a crispier top.

Let it cool for about 5 minutes before serving. Enjoy your homemade casserole warm.