Cook ground beef in a skillet over medium-high heat, breaking it up as it browns. Add onion and garlic, cooking until onion softens.
Season with salt, pepper, Worcestershire sauce, and beef broth. Simmer until broth reduces, leaving the beef moist and flavorful.
Spread butter on one side of each bread slice. Preheat a skillet or griddle over medium heat.
Place two slices of bread, butter side down, on the skillet. Layer with cheddar cheese, beef mixture, mozzarella cheese, and top with the remaining bread, butter side up.
Cook sandwiches for 3–4 minutes on each side, pressing gently until the bread is golden and the cheese melts.
Slice sandwiches in half, garnish with parsley, and serve warm. Enjoy!