Heat milk with spices and onion in a saucepan, and simmer gently for 20 minutes. Remove from heat, and allow flavours to infuse for an hour or so - 'bruise' the softened Cubeb peppers for extra flavour.
Strain the sauce, removing onion, whole spices, and any skin that has formed.
Reheat gently, add breadcrumbs, stirring 5 minutes or until liquid is absorbed.
Add cream, white pepper and salt to taste. Keep on a low heat 10 mins, stirring occasionally. Serve.
Make in advance
This sauce can be made in advance and reheated just before serving.