Place the currants, zest and juice in a bowl and set them aside to soak for at least 10 minutes.
Fill and boil the kettle. Lightly oil a 900ml/1½pt pudding basin.
Place the butter and sugar in a large bowl, then use an electric whisk to beat together until it becomes is light and fluffy.
Gradually add the egg, beating well between additions. Sift the flour and spice over the mixture and gently fold it in. Next, fold in the currants and juice. The mixture should now have a soft dropping consistency.
Spoon the mixture into the pudding basin. Place a 20cm/8in square of foil on the work surface, cover it with a square of nonstick baking paper then make a pleat in the centre of the two. Place it on top of the basin and fold the edges over to seal.
Stand the basin in a steamer and add boiling water from the kettle. Boil for 1hr 20minutes
Serve spotted dick hot with custard.