In a medium skillet set over medium-high heat, add the lean ground beef, breaking it apart as it cooks until browned, about 5-7 minutes. Add onion and garlic, sauté until soft, about 3-4 minutes.

Season with salt and pepper, Worcestershire sauce, and beef broth. Stir and let simmer for about 5 minutes until liquid thickens.

Butter one side of each slice of bread and preheat a skillet or griddle over medium heat.

Place two slices of bread butter-side down in the skillet. Layer with cheddar cheese, beef mixture, and mozzarella cheese. Top with another slice of bread butter-side up.

Cook for 3-4 minutes per side, pressing down with a spatula, until golden brown and cheese melts.

Remove sandwiches from skillet, slice in half, garnish with parsley if desired, and serve hot.