For the chocolate sauce, grease a 2-pint pudding basin with a little butter and set aside.
Place a large heatproof mixing bowl over a pan of simmering water (make sure it’s not too tight a fit or the steam will burn you). Add all of the sauce ingredients and allow to melt, stirring frequently until glossy. Remove from the heat.
Pour 8 tablespoons of the sauce into the bottom of the pudding basin and put the rest to one side for later.
For the pudding, finely grate the orange zest into a food processor (or mix by hand), add a pinch of sea salt and the remaining pudding ingredients. Blitz until smooth.
Gently transfer the mixture to the pudding basin, on top of the sauce.
Cover the pudding basin with some greaseproof paper and a layer of tin foil to hold it in place. Scrunch this around the edges and tie some string around the basin to secure it. At the same time, make a handle from the string so it is easier to handle the pudding basin later on.
When you’re ready to cook your pudding, get a saucepan large enough to hold the pudding basin and have its lid on tightly, so try it for size first.
Once you’ve got a good fit, place a heatproof plate on the bottom of the pan - this will stop the bottom of the pudding from burning.
Fill the pan with a couple of inches of boiling water from the kettle and carefully lower your pudding in – the water should come halfway up, so top it up, if needed.
Bring the water to the boil, put the lid on, then simmer for about 1½ hours, making sure you keep the water topped up when needed so it doesn’t boil dry.
After this time, carefully remove your pudding from the pan and turn out onto a nice big platter, but keep in mind that the chocolate sauce is going to be hot and runny, so be very careful.
Place the pudding in the centre of your table – delicious served with a jug of custard and the remaining chocolate sauce (warmed first). Top the pudding with a little holly and let everyone tuck in!