To make the mornay sauce, put the milk, parsley sprig, peppercorns, nutmeg, onion and bay leaf into a saucepan and bring to the boil. Remove from the heat, cover and leave to stand for 30 minutes.
Strain the milk into a jug, discarding the herbs and onion. Melt the butter in a saucepan, stir in the ﬂour and cook for 1 minute over low heat. Gradually stir in the milk and bring to the boil, stirring continuously until the sauce thickens. Reduce the heat and cook for 2–3 minutes. Remove from the heat and stir in the Gruyère and Parmesan cheeses and the cream. Season the sauce to taste.
I must be honest and say that I've never had mornay sauce before, so I really have no point of comparison or reference. However, I liked this, like it a lot actually! I used it on the Eggs Mornay recipe on this site, and the sauce certainly is mild. Took a little time, but it was time well invested. - 20 May 2013