1. In a large, shallow dish; whish together the eggs & milk; set aside.
2. Form two sandwiches with the bread & chocolate (break the chocolate to cover the bread without going over the edges); dip both sides of the sandwiches in the egg mixture to coat.
3. Heat butter in a large pan over medium heat; transfer the sandwiches to the pan. Cook, pressing occasionally with a spatula, until golden; about 1-2mins a side.
4. Transfer to a paper towel-lined plate. Cut each sandwich in half & dust with icing sugar before serving.