For the pudding, empty the first six cups and the nuts, if using, into a mixing bowl with the spices, then stir in the milk and egg. Once well combined, tip into a buttered 1.5 litre pudding bowl.
Cover with a double layer of buttered foil, making a pleat in the centre to allow the pudding to rise. Tie the foil securely with string, then place in a steamer or large pan containing enough gently simmering water to come halfway up the sides of the bowl. Steam, covered with a lid, for 2½ hours.
Check the water level during cooking, topping up if necessary. If you are preparing this pudding ahead, remove the foil, let it cool slightly, then wrap in cling film and then fresh foil. If you are serving it immediately, unwrap and invert onto a deep plate.
For the sauce, put everything in a pan and bring slowly to the boil, stirring. Allow to bubble away for 2-3 minutes, still stirring, until the sugar has dissolved and the sauce is pale caramel in colour and slightly thickened.
Remove from the heat. Pour the sauce over the pudding and decorate with the whole mixed nuts.
The pudding can be made 2-3 weeks in advance and frozen in the bowl - thaw it completely before reheating. It can also be made up to 3 days in advance and refrigerated. Just make sure you bring it to room temperature for an hour or so before reheating. The sauce can also be made a day ahead and kept in the fridge - simply reheat it in a small pan over a low heat. To reheat the pudding, cover with fresh foil and steam for 1 1/2 hours, or cover with cling film and microwave on High for 7 minutes.