Aubergine slices are the ideal filling for this superb vegetarian lasagne, which can be made a day in advance.
Parmesan cheese is not truly vegetarian, as it contains animal rennet. To make this dish 100% vegetarian, omit the cheese or find a suitable vegetarian substitute made without animal rennet. In supermarkets look for the 'parmesan style hard cheeses' which are suitable for vegetarians.
Steaming the aubergines for this dish avoids having to cook them in a large amount of oil, which they soak up like a sponge.