Cook the rhubarb with 75g/2¾oz of the sugar and the ginger over a gentle heat for 2-3 mins until just starting to soften. Remove from heat.
Grease a 900ml pudding basin. Put butter and remaining sugar in a bowl and cream together. Stir in vanilla extract, then beat in eggs, a little at a time. Sift in flour and carefully fold into the mixture.
Spoon rhubarb into the bottom of the basin, then spoon the sponge mixture on top and level off surface.
Butter a piece of greaseproof paper slightly bigger than the top of the pudding basin. Make a pleat in the centre and secure over the top of basin. Repeat with a piece of foil, then secure the whole thing with string. Place in a pan half filled with simmering water. Cover and cook for 1½ hrs, checking regularly that the pan does not boil dry. Remove cover, invert the pudding onto a plate, then carefully lift off the pudding basin. Serve with crème fraîche or single cream.