Preheat oven to 160°C Lightly grease a 22cm square ovenproof dish.
Arrange the waffles in the prepared dish. Sprinkle with the chocolate.
Whisk the eggs, sugar, milk, buttermilk and vanilla essence in a large jug until well combined. Pour half the egg mixture over waffles. Set aside for 5 minutes, then pour over the remaining egg mixture.
Place the dish in a large roasting pan and fill with enough boiling water to come halfway up the sides of the dish. Bake for about 50 minutes or until the custard has just set. Set aside for 5 minutes before serving. Dust with icing sugar and serve with ice cream if desired.