Method
In a heavy saucepan heat the butter or oil.
When the butter has melted or the oil is steaming, add half the broccoli.
Turn around a few times, then lower the heat and continue sautéing for about half a minute.
Add the flour and turn around till the mixture leaves the sides of the pan.
Remove from heat, and add the stock very gradually, stirring all the time (thus avoiding lumps).
Cool, and blend in a blender.
Place the pan back over the heat, and add the rest of the broccoli, milk, black pepper and celery salt.
Cook over high heat, stirring a few times, till it comes to a boil and then simmer over low heat for at least 10 minutes.
Serve hot garnished with cream.