# Trim the rhubarb and cut it into 2.5cm (1 in) strips. Put into a pan, and add about 2 tbsp water. Add the butter, sugar and ginger, and slowly simmer away until cooked, about 10 minutes. Remove and discard the ginger, and allow the rhubarb to cool.
# Take out a third of the rhubarb and drain through a sieve or colander, keeping the resulting juice. Put the juice on to the heat to reduce by about two-thirds, then cool.
# Meanwhile, divide the drained rhubarb between four glasses.
# Take the remaining rhubarb and purée in a blender or processor; do not make a fine purée, leave some texture.
# Whip the cream to soft peaks do not over-whip then sweeten with icing sugar to taste. Fold in the rhubarb purée. Using a piping bag with a 1cm (1/2 in) nozzle, pipe the fool mixture in a circular fashion into each glass. Chill for 2 hours only.
# Pour the reduced juice over the top of each glass, and serve.