Peel the onion, leaving it whole, then spike it with the cloves.
Put the spiked onion into a medium saucepan with the bay leaves, milk and a few pinches of sea salt and black pepper. Finely grate in a few scrapings of nutmeg.
Place the pan on a high heat and bring to the boil – keep a close eye on it as milk comes to the boil very suddenly. Reduce to a low heat and simmer very gently for 5 minutes to let the flavours infuse. Remove from the heat and leave to stand for 15 minutes.
Meanwhile, cut the crusts off of the ciabatta loaves. Tear 1½ loaves into chunks and pulse them in a food processor until you have coarse breadcrumbs.
Strain the milk through a sieve into a jug, discarding everything left behind in the sieve.
Return the milk to the pan and bring back to the boil over a high heat. Reduce to a medium heat and simmer, gradually stirring in the breadcrumbs until you’ve used them all up.
Add the butter and cream to the pan, stir well, then have a taste and season with a little more salt and pepper, if needed.
Have a look at the sauce – you want it to be the perfect consistency for you. If it’s too runny, blitz the remaining ciabatta and add some more breadcrumbs, if it’s a little thick, add more milk. Transfer to a jug or bowl and serve.
If you’re making this for another day, you want the consistency to be a little looser than you’d like as it will thicken as it sits, so add a bit more milk. When you’re happy with the consistency, spoon into a bowl and leave to cool. Once cool, cover the bowl with cling film and place in the fridge until Christmas Day.