Remove the stalks from the aubergines, slice them up into 1cm thick slices. Put to one side and season with salt, leave to drain.
Chop the onions. Heat the oil in a frying pan. Add the onions, season with salt and saute on a medium heat until they turn translucent and golden.
Add tomatoes, fresh basil, dried herbs, curry paste, wine, sugar, salt and pepper. Let it simmer for at least 15 minutes.
Brush off the salt from the aubergine slices and press the moisture out. Add to a hot frying pan with oil. Brown on both sides and set aside.
You’re now ready to layer up the gratin! In a deep dish, layer the tomato sauce followed by a layer of aubergines and then mozzarella. Scatter with the Guyere cheese. Repeat until you’ve used up all the ingredients, finishing with a little sauce. Scatter the top with the Parmesan cheese. Bake for 30 minutes until golden.