Sauté the mince and the finely chopped onion in a medium sized pot with a bit of water, deglaze with the wine, add 3 tbsp oil, the tomato, salt and pepper and boil for about half an hour on low heat. When it is ready, crumble the feta cheese in the pot. 

Oil a medium sized deep baking tray. Layer the potatoes cut into slices (about 1 cm thick). 

Wash the eggplants, salt them, cut them into strips and layer them on the tray over the potatoes.

Cover the tray with aluminum foil and place in a hot oven for about half an hour (or until the potatoes are tender). 

Take the tray off the oven and spread the mince mix on top. 

In the same pot (after rinsing it a bit, of course) prepare the bechamel. Melt the butter over low heat (take care that it doesn't brown!!!) and add the flour, whisking constantly. 

When the ingredients combine add the milk while cold, raise the heat and whisk until it thickens. 

Remove from heat, add the spices and the egg yolks dissolved in 2 tbsp milk and spread  in the baking tray, over the rest of the ingredients.

Bake the moussaka until the bechamel is golden brown.