Cut the aubergines into 1 centimeter thick slices and boil them in a big pot of salt water. Let them drain for at least one hour in a big sieve. Grate the mozzarella cheese. Prepare a béchamel sauce as described in the Lasagna recipe and add one quarter of the grated mozzarella and some nutmeg for extra spice.
Take a baking dish (about 13 x 9 inch big or 32 x 22 centimeters) and spread the olive oil over the bottom. Put half of the aubergine slices over the bottom of the baking dish. Sprinkle some grated mozzarella over the aubergines. If you want to add a layer of boiled potato slices, do it now. Then take your ragout sauce and spread it over the aubergines. Sprinkle with cheese again and lay out the rest of the aubergine slices. Cover with the béchamel sauce and spread the rest of the grated mozzarella (about one quarter of the full amount) on top of the béchamel sauce.
Bake in the oven for around 45 minutes at 190 degrees Celsius. The moussaka should be golden brown at the top. Let it rest for 15 minutes before cutting it. Moussaka also tastes very good cold.