Heat 2 tablespoons of oil in a large pan and sauté the onions over a medium heat until softened and beginning to colour, about 5 minutes.
Add the garlic to the pan, then add the aubergine and courgettes. Drizzle with a little more oil and continue to cook for 5 to 10 minutes, stirring frequently until they have softened slightly.
Add the peppers and cook for 5 minutes, stirring frequently.
Add the tomatoes, season with salt and pepper, then stir to combine. Cover and cook over a low heat for 30 minutes stirring occasionally until all the vegetables are tender.
Taste and add more salt and pepper if required. Tear the basil leaves into pieces and stir into the ratatouille. Serve from the pan or transfer to a warm serving dish and scatter a few small whole basil leaves on top.
Basil has a delicate flavour and is best added to the dish at the end of cooking. If the basil is young and has soft stems, these can be chopped and added to the dish earlier for extra flavour. If you use other herbs add with the tomatoes. Freeze: Ratatouille freezes well for up to 6 months.Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)