Place a steaming basket into a wide-bottomed pan, fill with water until it is just below the bottom of the basket, add the beans, salt and cook over a medium heat, covered, for approx. 15 mins. until just soft. Add the courgette for the final 2 mins. Remove the vegetables, allow to cool, place the vegetables in a large bowl. Add the celery and all the other ingredients up to and including the parsley, mix well.
Heat the butter in a frying pan until it foams and smells slightly nutty. Place in a bowl and allow to cool slightly. Stir in the remaining ingredients, pour vinaigrette over the salad, serve immediately (see note).