Cut the crust off from the white sandwich bread slices.
Brush the bread with béchamel sauce for the Sicilian version, add a slice of ham for the roman way or leave it plain for the Neapolitan. Add 2 thick mozzarella slices (about 1-inch wide) and close the sandwich.
Arrange flour in a bowl or plate, and dredge the mozzarella sandwich in until fully coated.
Beat eggs and milk in another bowl, season to taste with salt and pepper. Coat the sandwich on all sides with the egg-wash until fully covered.
Arrange breadcrumbs on a plate and coat the sandwich to fully seal the mozzarella inside and avoid leaks during frying process.
Heat the oil a in a deep heavy sauce-pan or a wok. Add more oil if needed until is enough to deep-fry the sandwich.
Heat over medium-high heat until a deep-fry thermometer reads 350°F/ 170°C.
Gently fold the sandwich in and deep-fry 2 mins on each side, or until crispy and golden on both sides.
Drain on kitchen paper and serve nice and hot. Enjoy!