One of my favourite dishes is Parmigiana di melanzane: layers of aubergine, tomato sauce, mozzarella, and parmesan. But it is let down by many brands of mozzarella, which toughen when cooked. Another favourite is moussaka, particularly when it has a buoyant, cheesy topping. Let's perm them.
1 clove garlic, chopped
1 400 g tin tomatoes
28 g butter
28 g flour
250 ml milk
2 heaped tbsp pecorino
1 egg yolk
Cut the aubergine into rounds about 5 mm thick. Brush them with olive oil (I pour the oil into a saucer, and brush the aubergines with the tines of a fork), put them in a roasting tin, season, and bake at gas mark 6/200 C for 20 to 30 minutes, or until soft. (There is more on cooking aubergines here.)
Soften the garlic in a saucepan with another tbsp olive oil. Pour in the tomatoes, breaking them up with a wooden spoon as they cook. Add a little salt, and simmer until the sauce is sludgy. (This is a very basic sauce. You might begin with a base of onion, celery and carrot; you might add herbs.)
Make a bechamel. Melt the butter in a small saucepan, add the flour, and cook for a minute or so; don't let it go brown. Pour in the milk gradually, stirring to incorporate each portion before adding the next. Let the sauce bubble for a minute or two, stirring constantly, then turn off the heat. The sauce should be quite thick. Stir in the cheese (you might use any hard cheese -- cheddar would be fine), then the egg yolk (which would scramble if added to the boiling sauce). Add nutmeg and pepper; you should not need salt.
Unless your gratin dish has a small base, you may not have enough ingredients to form several layers. When I made this dish the other night, I simply poured in the tomato sauce, arranged the aubergine slices on top, and finished with the cheese sauce. I baked it at gas mark 4/180 C for 30 minutes, after which the topping was brown and, thanks to the egg, pleasingly puffed up.
We ate this when it was lukewarm, an hour later. It was at its best then, I think; but it would also have been delicious hot, or cold.