Bring the white chicken stock to simmering in the medium pot.
Temper the roux with a little stock and then mix with the rest gradually, whisking constantly. Do not let it boil.
Add the bouquet garni and skim any impurities from the surface of the liquid - écumer.
When the velouté is coating the back of a spoon, remove the bouquet garni, season to taste, and strain the sauce.