Cook the beef in a large skillet over medium-high heat, breaking apart for about 5-7 minutes until browned. Add chopped onion and minced garlic, sauté until onion is translucent, about 3-4 minutes.

Season beef mixture with salt and pepper. Stir in Worcestershire sauce and beef broth. Let it simmer for 5-6 minutes until flavors deepen.

Butter one side of each slice of bread. Preheat skillet or griddle over medium heat for about 2 minutes.

Place two slices of bread in the skillet, butter side down. Layer with cheddar cheese, cheesy ground beef mixture, and sprinkle with mozzarella cheese. Top with remaining slices of bread, butter side up.

Grill for 3-4 minutes on one side. Press down with a spatula for even melting. Check for golden brown underside.

Flip and grill for another 3-4 minutes until golden brown and cheese is melted.

Remove sandwiches, slice diagonally, and garnish with chopped parsley if desired. Serve hot.