Bring the milk to a boil in a saucepan with the onion, bouquet garni and clove. Cover and leave to infuse for 10 minutes. Make the roux: Melt the butter in a heavy saucepan. Whisk in the flour and cook until foaming, about 1 minute. Remove the pan from the heat and let it cool slightly. Strain in the hot milk, whisking constantly. Return
the sauce to the heat and bring it back to a boil, whisking constantly until the sauce thickens. Season to taste with nutmeg, salt and pepper and simmer for a further 2 minutes.
