Slice the mushrooms thickly. Put them into a pan with the cold milk (and cream if using). Three-quarters cover the pan and bring quickly to a fast simmer. Add the bay leaf and a little salt and reduce the heat to very low. Three-quarters cover the pan again and leave to stew gently for 5-6 minutes. Strain to separate the liquid from the mushrooms, discard the bay leaf and keep the mushrooms warm in a very low oven.
Make a smooth rich sauce with the butter, flour and creamy mushroom cooking liquor. Stir in at least 1/2 teaspoon each tarragon vinegar and anchovy essence. Leave to simmer for 2-3 minutes then season to taste with salt and pepper. Quickly stir in the queens and immediately reduce heat to low. Half cover the pan and cook for just 5 minutes. Stir occasionally during this time and be sure to keep the heat very low - only a very occasional bubble should break the surface of the sauce or the shellfish may toughen.
Draw the pan away from the heat, quickly stir in the mushrooms and check seasoning. Then turn the contents of the pan into a warmed gratin dish (or divide it between warmed scallop shells for an elegant first course). Sprinkle with parsley and garnish with fried crumbs or triangles of fried bread. Serve alone as a first course, or as a main course accompanied by some green beans and a little rice or a loaf of warm French bread.
Serves 2 as a greedy feast, 3 as a main course, or 6 as an appetizer.