Start by spreading a layer of mayonnaise to taste all over a slice of crustless bread.
Add 1 slice of ham, 1 slice of cheddar cheese and top it with another slice of crustless bread.
Then, add another layer of mayonnaise to taste, +1 slice of ham, 1 slice of mozzarella cheese and finish by topping everything with +1 slice of crustless bread.
Repeat this process with the other slices of bread and the filling we prepared.
In a medium bowl, add the eggs, the milk, the salt and mix.
Dip the sandwich we prepared into this egg mixture.
In a skillet over medium heat, add the butter and stir until melted.
Add the sandwich we prepared and let it fry until golden brown on all sides.
Turn the sandwich over using 2 spatulas and repeat this process with the other sandwich.
Serve.