Sprinkle both sides of the aubergine slices with salt. Place slices in a colander, and place a dish underneath the colander to capture liquid that will sweat out of the aubergine. Allow to sit for 30 minutes.
Preheat oven to 180 C / Gas 4. In a medium bowl, mix the ricotta, mozzarella cheese and 1/2 of the Parmesan cheese. Mix in egg and basil.
Rinse the aubergine in cold water until all salt is removed. In a large frying pan, heat 4 tablespoons olive oil over medium heat. Place one layer of aubergine in the pan, brown each side. Repeat with remaining aubergine slices, using additional oil if necessary.
In a 20x30cm baking dish, evenly spread 1/3 of the pasta sauce. Arrange a single layer of aubergine slices on top of the sauce. Top the aubergine with 1/2 of the cheese mixture. Repeat layering process until all the aubergine and cheese mixture is used. Pour remaining sauce on top of layers, and sprinkle with remaining Parmesan cheese.
Bake 30 to 45 minutes in the preheated oven, until sauce is bubbly.
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.