Preheat oven to 180C (160C Fan)/Gas 4 and lightly grease a wide ovenproof dish with a little butter. Pour the orange juice into another wide, shallow dish and add the zest. Butter each half hot cross bun on both sides before soaking each one thoroughly in the juice and zest mixture. These can be left to soak while you make the custard.
Put the milk and cream into a pan over a low heat, until hot but not boiling. Whisk the eggs with the caster sugar in a jug and then slowly pour the milk mixture over the eggs, stirring until smooth. Add the orange liqueur, if using.
Arrange the bun halves in layers, overlapping slightly, and sprinkle over the dried fruit in between each layer, until the fruit and buns are all used up. Pour the custard over the pudding and sprinkle with the golden caster sugar and cinnamon. Bake for 25-30 minutes until the custard is set and the pudding is golden brown.
Serve straight away, with a spoonful of Trewithen Dairy Cornish Clotted Cream.