Put pieces of celery in water, bring to boil, then simmer for 15 minutes. Drain and reserve celery. In a fresh saucepan, cook the heads and tender parts of leeks until 1/4 of the water has boiled away.
For the sauce, combine pepper, stock and honey, and add to strained celery stock. Bring to boil and simmer for 25 minutes to reduce. Put the cooked leeks into a new saucepan and pour the sauce over them. Heat the sauce with the leeks and serve.
The celery stalks may be added, if you wish.
Source - The Roman Cookery of Apicius