Preheat oven to 180C / 325F / Gas 4
Butter each slice of bread, and any 'knobs', 'heels' 'crusts' or 'end bits' you have kept back and cut into triangles.
Zest the two oranges and squeeze the juice into a large jug (you should get about 100ml from 2 small oranges)
Roughly chop the chocolate.
Add 500ml milk, caster sugar and the two eggs to the jug with the orange juice, whisk to combine.
Start to build the first layer of your pudding, this bits quite therapeutic, bit like making a jigsaw puzzle. Sprinkle over half the chocolate and some of the orange rind.
Repeat point 5, this time use up all the chocolate but leave a pinch of zest left to sprinkle on the top layer.
Add the final layer, this can be in a pattern, or not, whatever takes your fancy. Now pour over the custard mixture making sure you get every piece of bread soaked. Sprinkle the remaining zest and demerera sugar to decorate.
Now you're going to think I've gone mad because I'm going to ask you to weight it down for an hour! I find this helps with the soaking process and prevents the top layer from becoming rock hard during the back. This is how I weight my pudding down;
Once an hour has passed cover with foil and pop the pudding into the oven for 30mins, after half an hour, remove the foil and bake for another 20mins so the top becomes golden brown and caramelised.