Begin making your pudding the day before steaming it. Place all of the ingredients from the ‘to soak overnight’ list in a bowl, mix well, cover and set aside overnight.
The next day generously grease a 1.2 litre pudding basin with the 1 tablespoon light olive oil, then place a square of baking paper (6 x 6 cm) in the bottom, pressing down well to adhere it to the greased basin. This will help the pudding release from the basin when you serve it.
Sift the flour and baking powder in to the previously soaked ingredients, then mix together well to form a thick batter.
Pour your batter in to the basin. Cover the basin’s top with a layer of greaseproof paper, then a layer of aluminium foil. Secure these tightly in place with an elastic band around the basin’s rim.
Place the basin on a trivet in your slow cooker, then add boiling water to roughly 1/3rd the way up the sides of the basin. Put the cooker’s lid on and cook on high for 6 hours (if using a multi-cooker set it to just below 100 °C). After cooking turn off the slow cooker, but leave the water and pudding in there until cool.
Once cooled, remove the pudding, replace the paper and foil with fresh pieces and secure with elastic band. Store your pudding in a cool, dry place for 6-8 weeks to mature.
Before serving reheat the pudding by placing it (still covered in the paper and foil it was stored in) in the slow cooker, then add boiling water to roughly 1/3rd the way up the sides of the basin. Put the cooker’s lid on and heat on high for 2 hours (if using a multi-cooker set it to just below 100 °C). Run a flexible spatula around the pudding’s edges to separate it from the basin, then turn out carefully on to a plate and remove the square of baking paper. Optional: 2-3 tablespoons of warmed brandy can be poured on.