1 -In a frying pan put the oil, the beef, the tomato paste, cumin, black and white pepper, nutmeg and some salt and start frying forcing the meat with a fork to fall apart into crumbs.
2 -When all the meat is falling apart remove from the fire and drain the excess fat (although you could also add it to the baking tin).
3 -Peel the potatoes and chop them into small pieces (1/2" or a bit smaller).
4 -Put half of the potatoes in a deep baking tin, spread the meat mixture over them and top it with the rest of the potatoes; you could use a larger or a smaller diameter tin depending on how thick you want your moussaka to be.
5 -Add water until only half of the top layer of potatoes stays uncovered by it and break the stock cube over it (BE CAREFUL – if you opt not to use the cube you’ll have to add some salt).
6 -Preheat the oven to a medium temperature and put the moussaka in.
7 -In a bowl beat the yogurt with the eggs the thyme, a bit of salt and some black or white pepper if you want.
8 -When the water in the tin starts boiling and the potatoes start to cook, poor in the yogurt mixture taking care that it covers the potatoes entirely.
9 -Bake until the potatoes are done (about 45 min-1 h total baking time) but be careful not to burn the yogurt lid – you may want to lower the heat or to leave the oven heating from under the tin only.
10 -When ready take out of the oven and leave to cool a bit – potatoes cool very slowly.
11 -Serve very warm.