1. Cut the celery hearts (trim off the leaves) in half and wash in cold water.
2. Place the lemon juice, water, oil, herbs and seasonings in a pan and bring to the boil.
3. Place the celery halves in it and poach covered until tender, approximately 20 minutes, depending on size. Drain well and cool.
4. When completely cold arrange the halves on a serving dish.
5. Mix together the mayonnaise and vinegar and coat each of the halves. Decorate each with 2 anchovy fillets and a black olive.