Melt the butter in a large, heavy pan and cook the onion for 5-8 minutes until soft but not
browned, stirring from time to time. Add the Jerusalem artichokes to the pan and stir until coated
in the butter. Cover and cook gently for 10-15 minutes, being careful not to allow the artichokes
to brown. Pour in the chicken stock and milk, then cover and simmer for 15 minutes. Cool slightly,
then process in a blender or food processor until smooth.
Strain the soup back into the pan. Add half the cream, season to taste and reheat gently.
Lightly whip the remaining cream and the saffron powder. Ladle the soup into warmed soup bowls and
put a spoonful of saffron cream in the centre of each. Sprinkle the chopped chives over the top and
serve at once.