Fry off a stick of celery, a carrot and an onion all finely chopped with a clove or three of garlic. When soft add passata and some dried oregano and cook off for a few minutes.
This is how I learned to make it...
Slice aubergine not too thin...,maybe .5 inch thick. Dip into flour,then beaten egg...fry in olive oil until golden.You can also just fry in the oil.
Make a tomato sauce by gently sauteeing some crushed garlic and diced onion until soft. Add to this some basil and oregano,and a carton of passata. Let simmer gently for 30 minutes.
Spread some sauce in the bottom of a oiled tin. Lay a layer of aubergine,sliced mozzarella,and grated parmesan, topped with tomato sauce. Continue until all is used up. Bake in the oven for about 35-45 minutes. Let cool slightly before slicing.