Alright. So, I've googled a bit and "derived" my own recipe. FWIW, the first time I've done it (the pictured one), I've employed the technique of cooking Lasagna according to Hazan (i.e. mix the meat sauce with the béchamel). The second time I've done a more "classic" Moussaka, that is add cheese to the béchamel, then thicken it with two eggs, and add all of it on top of the eggplant/meat sauce-layers. Both are different, both are good. Anyway, there are many different techniques employed in the recipes I've seen.
Anyway, on to "my" recipe. For my dish, I've used:
700-900g minced lamb meat (you can use beef, but I think it's more authentic with lamb, plus it tastes great)
3-4 medium/large eggplants
1-2 medium onions chopped finely
1-2 cloves garlic (optional)
Some parsley (optional)
1-2 400g can of plum tomatoes
Ground sweet paprika
50g grated Parmigiano
Now on to the probably most impactful part of the mousska. The eggplant.
Slice the eggplant lengthwise into 0.5-0.75 cm thick slices. Salt them generously on both sides. Let sit for 10 minutes, preferrably longer. Pat dry, maybe with some pressure to squeeze out some more water. Heat up the broiler of the oven (alternatively, heat up the oven to 200°C). Brush the eggplants on both sides with olive oil and add pepper. Roast the slices in the oven until browned, then flip the slices and repeat. They'll lose a lot of volume that way. Repeat with the remaining eggplants (you'll likely have to do two, maybe three batches--probably the most time intensive part). [other recipes employ different techniques ranging from not salting the eggplants over frying them in olive oil or battering and then frying them in olive oil]
Meanwhile, heat some olive oil in a pan on medium heat. Add the chopped onion along with the cinnamon (to taste, 1-2 tsp or so), ground cumin (to taste, 2 tsp or so) and ground sweet paprika (to taste, 1 tbsp or so). Sweat for 8 minutes. Add the garlic and parsley (you can also add some harissa or tomato purée at this point). Sweat for 2 minutes or so, then add the minced lamb meat, salt, pepper, some cayenne or chili. Cook until the lamb has lost its rare colour, then add the plum tomatoes (chopped up if you use wohle ones). Let simmer for as long as possible. You'll want a sauce that doesn't have much liquid left. Adjust seasoning at the end. If the minced lamb meat was fatty, you might remove some fat if you care about such things.
Meanwhile prepare the béchamel. Add a generous amount of ground nutmeg at the end and salt it.
Now, as I've said earlier, I've employed a technique similar to Hazan's Lasagna recipe in the pictured Moussaka.
Add some béchamel to the bottom of the dish. Add the remaining béchamel to the meat sauce and mix it together but reserve some to top the moussaka with (as much as you used for the bottom layer). On top of the bottom layer, add a layer of eggplant slices, then half the meat sauce, then a layer of eggplant slices, the rest of the meat sauce and another layer of the eggplant slices. Top with the rest of the béchamel, the grated parmigiano and some butter flakes. Add to the oven (preheated to 200°C) and bake for about 30 minutes, until nicely browned (if it browns too quickly, add some aluminium foil on top and finish baking for some more minutes.) Turn of the oven, open it slightly and let the moussaka rest for 15-30 minutes. Serve.
To sum it up, there are lots of variations possible. If you want to prepare the more classic version, do this:
prepare the béchamel, add a generous amount of nutmeg, some salt and the ground cheese. Stir until desolved. Let cool slightly, then add two beaten eggs and beat until you have a uniform sauce. Add some to the bottom of the dish, then the aubergine layer, half of the meat sauce, aubergine layer, other half of the meat sauce, aubergine layer and top witht the rest of the béchamel. Bake in the oven (200°C) until sufficiently browned (again, (partially) cover with tin foil if it browns too quickly), then let rest for 15-30 minutes.
butter the dish (fwiw, I still like to add a layer of béchamel in this version), add a layer of eggplants, half the meat sauce, layer of eggplants, half the meatsauce, layer of eggplants.
Sorry for the wall of text but it's not that easy to describe.