A Provençal vegetable stew best served at room temperature, ratatouille should be a very basic preparation and not over-refined. Bad variations (vegetables diced too small, too much tomato, using dried herbs and so on) often debase one of the finest combinations of Mediterranean flavours.
It is very important to use the best extra virgin olive oil and to cook all the different vegetables separately, combining them only at the last moment The aubergines and courgettes must be very fresh - when they have spent too long on the shelf they go bitter. Some texts advise salting them to remove bitterness, but experience suggests that all this delivers is old, salty and bitter vegetables.
Making a first class ratatouille takes time - there are no short cuts. It is vital not to fry the ingredients quickly, but to stew them gently and avoid overcooking. The ratatouille improves after a day's rest to allow the flavours to amalgamate.
Alternatively, ratatouille while still hot is delicious mixed with an equal quantity of fusili or macaroni (or any other robust dried pasta). Simply cook the pasta, drain and toss it with the ratatouille while it is still warm. Dress with torn basil to serve.