01 -
Heat a medium skillet over medium-high heat. Add ground beef and cook, breaking up the meat with a spatula until evenly browned. Add the finely chopped onion and minced garlic; continue cooking until the onion is softened and translucent.
02 -
Season the mixture with salt and freshly ground black pepper. Stir in Worcestershire sauce and beef broth. Reduce heat and simmer, stirring occasionally, until the liquid is mostly absorbed and the filling has thickened.
03 -
Spread softened butter on one side of each bread slice. Preheat a skillet or griddle over medium heat.
04 -
Place two bread slices, buttered side down, onto the skillet. Top each with half of the cheddar cheese, an even layer of the beef mixture, and half of the mozzarella cheese. Close with remaining bread slices, buttered side up.
05 -
Cook the sandwiches for 3–4 minutes per side, pressing gently with a spatula, until the bread is golden brown and the cheese is fully melted. Slice in half, garnish with chopped parsley if desired, and serve immediately.