Preheat the oven to 160C/140C fan. Grease your baking dish (see note) with some of the butter and sprinkle half of the demerara sugar into the dish followed by a sprinkling the cinnamon also.
In a small pan heat the milk with the orange zest until hot but not boiling and then leave to cool.
Butter the pannetone with the remaining butter. Make your custard mixture by whisking the eggs and sugar together until the sugar is well mixed then add the infused milk, cream, vanilla essence and orange juice.
To build your pudding dip each of the pannetone slices in to the custard mixture and build up in your greased baking dish. Once built slowly pour the remaining custard mixture over the bread then sprinkle with the remaining demerara sugar.
Place in to the preheated oven and bake for 35 to 40 minutes. I would check after 35 minutes. It should be cooked in the middle with no runny custard but just set with a lovely wobble. If not cook for a few minutes more until ready.
Serve with a double cream or custard, whichever you fancy.