Generously grease a 1 to 1.2 litre pudding basin and place a small disc of baking parchment in the bottom. Put the kettle on.
Whisk together the butter, sugar and orange zest until pale and fluffy then whisk in the eggs one at a time, adding a spoonful of the flour with each one.
Once the eggs are combined, sift in the rest of the flour, the ground ginger and the salt and fold through. Add the chopped stem ginger and mix in.
Transfer the batter to the prepared pudding basin and level the top. Make sure that there is a gap of at least an inch between the batter and the top of the basin to allow for expansion.
Place an upturned saucer in the bottom of the slow cooker and place the pudding basin on top. Pour enough freshly boiled water into the slow cooker to come 2/3rds of the way up the sides of the pudding bowl.
Place the lid on and cook on high for four hours. Once cooked the pudding should be firm to the touch and a skewer inserted into the centre should come out clean. If it is still undercooked, replace the baking parchment, foil and string and cook for another hour.
Once cooked, remove the string and parchment. Place a serving platter on top of the basin and flip the whole lot over. Carefully lift off the basin, top with the candied orange slices and syrup and serve straight away with custard or ice cream.
While the pudding is cooking make the candied orange slices and syrup. Place the blood orange juice in a measuring jug and add enough water to take it up to the 250ml mark.
Place the juice in a small saucepan with the sugar. Cook over a gentle heat, stirring regularly until the sugar has dissolved.
Add the orange slices and bring up to a gentle simmer. Cook for about 45 minutes to 1 hour, until the oranges are soft and the peel has turned slightly translucent. Stir them every now and again to make sure that they are evenly covered with syrup.
Remove from the heat and set aside to cool. They can be stored in an airtight container in the fridge for up to a week.