Preheat the oven to 180 deg C/Gas 4.
Combine the eggs, cream, milk, castor sugar, orange zest, cinnamon and vanilla paste in a medium bowl and whisk really well to combine all the ingredients properly.
Spread both sides of the slices of panettone with a thin smear of butter. Trim the cake slices to fit an ovenproof dish. Spoon the brandy over the cake and layer all the slices, sprinkling each layer wiith brandy as you go. Pour the cream mixture evenly over the layered, brandied slices and scatter the demerara sugar over the pudding.
Bake the pudding for about 35 minutes or until the custard has set and it has turned a mouth-watering golden colour. Serve with a dusting of icing sugar and a large dollop of lusciously decadent thick cream.