Use a sieve or a slotted spoon to remove the vegetables and bay from the milk (if using a sieve, don't forget to put a bowl underneath when you pour it out!). Return the pan to a low heat, and add the breadcrumbs and butter. Cook for a minute or two until the breadcrumbs have cooked right into the milk, and season generously with salt and pepper. Serve warm. You can make the sauce in advance and reheat in the microwave if necessary.