Preheat the oven to 180°C.
Grease a 1,75 litre baking dish with butter. Spread the bread with butter, remove the crusts and cut the slices in half diagonally.
Whisk the egg yolks with the sugar.
Heat the cream and milk together in a saucepan over a low heat. Add the chocolate and mix slowly until combined. Do not allow the mixture to heat above a simmer.
Pour the chocolate, milk and cream mixture slowly through a sieve onto the yolk mixture, stirring all the time.
Arrange the bread in layers in the greased dish. Sprinkle the cranberries between the layers as you go. (The cranberries have a tendency to burn, so make sure the final layer of bread does not have cranberries on top of it.)
Pour the warm chocolate egg custard over the bread. Leave the custard to soak into the bread for 15 to 25 minutes.
Place the dish in a roasting tray and fill the tray with enough boiling water to reach just below the rim of the baking dish. Cover the tray with lightly buttered tinfoil. Bake in a preheated oven for 20 to 30 minutes, or until the custard begins to thicken.
Sprinkle castor sugar over the pudding and place under the grill for a few minutes to caramelise. Serve hot
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