Pour the milk into a saucepan and add the onion, salt, peppercorns, nutmeg cloves and bay leaf. Bring the milk to the boil reduce the heat to the lowest possible and simmer for 15 minutes.
Remove the crusts from the bread and use a kitchen machine or grater to turn it into breadcrumbs.
Remove the onion, peppercorns and bay leaf. Add the butter and breadcrumbs and cook over a very low heat, stirring frequently, for a further 10-15 minutes. If the sauce is too thick, add a little more milk.