This classic sauce is known in Italy as Salsa Balsamella, and was used in Italian cooking long before it made its appearance in France. This recipe gives the béchamel the smooth coating consistency which is right for most pasta dishes. It can be made thicker or thinner by using less or more milk.
In a small saucepan heat the milk (with the bay leaf, if used) to just below a simmer.
Melt the butter over a low heat in a heavy saucepan. When it bubbles (do not let it brown) add the flour and cook for a few minutes without allowing it to discolour. This helps to get rid of the floury taste. Remove from the heat and whisk in the milk gradually. Return to the heat and stir until thick