Cut the onion in half and stud with the cloves. Place in pan along with milk, bay leaves and peppercorns. Add salt and pepper and bring all to the boil, stirring constantly. Once mixture starts boiling, remove from heat and let sit at least 2 hours, or overnight in fridge, to infuse flavours.
To finish the sauce, strain milk and place back in pan and warm over medium heat. Stir the breadcrumbs and add half the butter. Stir often, until sauce has thickened. Add whipping cream and remaining butter. Season with nutmeg and more salt and pepper, if neccessary. (The consistency should be that of soft porridge). Serve alongside with roast turkey or chicken.