Pour milk into a small saucepan. Add bay leaf, onion and peppercorns. Bring to just a boil, then remove from the fire and leave aside.
Put chicken mince in a non-stick saucepan and fry briskly to brown the meat. Add the onion. Toss well and cook until onion turns soft. Stir in tomato purée, basil, oregano and water. Cover the saucepan with a lid and cook over a medium low heat for 8-10 minutes. Add salt and pepper to taste.
Melt butter in a clean saucepan. Stir in flour and cook until it turns frothy. Bring saucepan away from the heat and strain in the cooled flavoured milk. Bring the saucepan back to the fire and whisk until the white sauce begins to boil and thicken.
Lightly grease a straight-sided ovenproof dish. Line the base of the dish with one layer of lasagna sheets. Spread on a thin layer of the white sauce. Add a layer of the cooked minced meat. Repeat the layering until all the lasagna sheets and cooked mince are used up, finishing with a layer of lasagna sheets. Sprinkle with Parmesan and parsley.