Pre-heat the oven to 170°C. In a pan, heat the olive oil over a moderate heat and sauté the lamb mince until brown. Remove the mince from the pan and set aside. Add the onions and garlic and sauté until soft, add the mince to the pan. Add the tomatoes, 150ml water, wine, parsley, seasoning and nutmeg and simmer for 30 minutes until almost dry. In a frying pan, heat some oil over a moderate heat, add the aubergines and sauté until coloured on both sides. Grease a casserole dish and arrange half of the aubergines on the base. Add the mince mixture and the rest of the aubergines over the top. In a saucepan, heat the butter, add the flour and stir for a few minutes. Add the milk gradually, stirring continuously until it begins to thicken. Season to taste. In a bowl, mix together the egg yolk and cream followed by the white sauce and half of the grated cheese. Pour over the aubergines and add the rest of the grated cheese. Place in the oven and bake for one hour, serve with seasonal vegetables or a light salad.