Pre-heat a waffle iron to medium heat.
In a shallow bowl, whisk together the eggs, milk, mustard, salt and pepper.
Brush the waffle maker with the melted butter. Build the sandwiches: one slice of bread, some cheese, a slice of ham, a slice of turkey, more cheese and another piece of bread. Turn the sandwiches in the batter and place in the waffle iron. Close the waffle iron and cook for 5 minutes, or until golden brown.
Serve with an arugula salad alongside.