In a medium skillet over medium-high heat, brown the ground beef for about 5–7 minutes, breaking it apart as it cooks.

Add the chopped onion and minced garlic to the skillet, cooking until the onion is soft and translucent, about 3–4 minutes.

Season with salt and pepper, stir in the Worcestershire sauce and beef broth, and simmer for about 5–7 minutes until thickened.

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

Place 2 slices of bread, butter side down, in the skillet. Layer with cheddar cheese, beef mixture, and mozzarella cheese, then top with remaining bread slices, butter side up.

Cook each side for about 3–4 minutes, pressing down gently until the bread is golden brown and the cheese melts.

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