Warm the milk with the vegetables, herbs, salt and spices, and bring it slowly to simmering point. Put a lid on the pan and stand it in a warm place on the cooker to infuse for ½ hr. Strain the milk, melt the butter, add the flour, cook this roux for a few minutes without browning it. Stir the flavoured milk gradually into the roux. Bring the sauce to boiling-point, stirring vigorously. For an extra smooth result, wring the sauce through damp muslin. If cream is used, add it to the sauce just at boiling-point and do not reboil it.
Serve with chicken, veal, fish or white vegetables.