Source: BBC Food: Cheats Moussaka
Boil the potatoes whole for 20 mins or just until tender. Drain and allow to cool.
Return the pan to the heat and add 2 tbsp olive oil and the onion. Cook until softened, then add the lamb. Fry the mince for 5 mins or until cooked through and starting to char. Add the garlic and spice, and stir in the passata. Bring to a simmer, then season to taste, take off the heat and set aside until needed.
Heat oven to 220C/200C fan/gas 7. Warm a griddle pan over a high heat and brush a little oil over the aubergines. Grill for 2-3 mins each side or until char lines appear. You may have to do this in 3-4 batches.
Once cool enough to handle, cut the boiled potatoes into thick slices. Put 1 tbsp oil in the base of a deep ovenproof dish and start with a layer of potatoes, then aubergines, a sprinkling of seasoning, then a layer of the lamb mixture. Repeat until all the mixture is used up, ending with a layer of aubergines. Spread the crème fraîche over the top and scatter with the cheese. Put in the oven for 10 mins or until the cheese is golden.