1. In a heavy saucepan heat the butter or oil.
2. When the butter has melted or the oil is steaming, add the vegetables.
3. Turn around a few times, then lower the heat and continue sauteing for about half a minute.
4. Add the flour and turn around till the mixture leaves the sides of the pan.
5. Remove from heat, and add the stock very gradually, stirring all the time (thus avoiding lumps).
6. Add the milk, black pepper and celery salt.
7. Bring to a boil and then simmer over low heat for at least 10 minutes.
8. Serve hot garnished with cream.