Tip the dates into a bowl with the raisins, cover with 200ml hot water from the kettle and set aside. Meanwhile, grease a 1.5 litre pudding basin and line the base with a disk of parchment paper. Put the dry ingredients and orange zest in a large bowl. Stir in the dates and raisins (and soaking liquid), the rose and orange water, with the eggs and butter. Mix until everything is combined. Tip into the basin and cover with a circle of parchment paper, then foil, then tie the rim with string.
Place the pudding on an upturned jar lid in a large pan and pour in hot water from the kettle until it comes halfway up the bowl. Cover the pan and gently steam for 4 hrs, topping up with more water if needed. The pudding can be eaten straight away, chilled and kept for up to a week, or frozen for 1 month. To reheat, defrost completely or remove from the fridge and steam pud again for 30 mins until piping hot.
To make the butter, whisk the ingredients together. Serve the pudding in wedges with a spoonful of the butter melting over it.