Preheat the oven to 180ºC/160ºC fan/gas mark 4. Using an electric mixer, combine the Dark Muscovado Sugar with the butter until light and fluffy.
Add the flour, baking powder and spices, and then mix again until combined. Slowly add the eggs, followed by all the remaining ingredients for the pudding, mixing together as you go.
Divide the mixture between the pudding moulds and transfer to a large roasting tray. Top each surface of the batter with another circle of baking parchment, then cover each with a square sheet of foil (roughly 10cm), then scrunch the foil around the rim making sure it is airtight.
Transfer the roasting tin to the oven and fill with boiling water from the kettle so that it comes roughly halfway up the side of each pudding mould. Cook for 45 minutes, or until springy and firm to the touch in the centre.
Meanwhile, make the spiced rum mascarpone cream. Beat all the ingredients together in a bowl and store in the fridge until ready to serve with the Christmas pudding.