Start by heating your skillet over medium-high heat. Once it's hot, add the ground beef. Use a spatula to break it apart as it cooks until browned, about 5-7 minutes.

Once your beef is browned, toss in the finely chopped onion and minced garlic. Stir and sauté until the onions become translucent, about 3-4 minutes.

Season the mixture with salt and pepper, then add the Worcestershire sauce and beef broth. Stir and let it simmer until the liquid reduces and thickens slightly, about 3-5 minutes.

Spread softened butter on one side of each slice of bread. Preheat another skillet or griddle over medium heat.

Place two slices of bread on the skillet with the butter side down. Layer on half of the shredded cheddar cheese, followed by the beef mixture, then top with mozzarella cheese. Place the other slices of bread on top with the butter side facing up.

Cook each side of your sandwich for about 3-4 minutes until golden brown and crispy. Use a spatula to gently turn them.

Once both sides are grilled, let them cool for a minute before slicing in half. Optionally, sprinkle fresh parsley on top.