Make crumbs. Cut the crusts off the bread. Blitz it in a food processor until fine, then weigh out 110 g.
Stud onion. Push 3 cloves into each onion half.
Heat milk. Put the milk, onion, bay leaf, peppercorns and salt in a medium saucepan. Warm over a medium heat until the milk just starts to simmer.
Infuse milk. Take the pan off the heat, cover and leave for 1 hour. Leave for up to 2 hours for a stronger flavour.
Strain. Lift out the onion, bay leaf and peppercorns.
Add crumbs. Put the pan on a low heat. Stir in the crumbs and half the butter (25 g).
Cook gently. Cook for about 10 minutes, stirring often, until the crumbs have broken down and a spoon leaves a slow trail.
Finish sauce. Stir in the cream and the remaining 25 g butter. Add the nutmeg. Taste, then season with salt and pepper. Add a splash of milk if too thick.
Serve warm. Pour into a warm jug. Serve straight away, or cover and keep warm off the heat until needed.