To make the sauce, peel and finely slice the garlic cloves. Pick the basil leaves and finely slice the stalks.
Heat a good couple of lugs of oil in a large pan over medium heat, add the garlic and basil stalks. Pierce the chilli once with a knife so it doesn’t explode when frying, then add to the pan. Fry gently until the garlic is soft but not coloured, stirring occasionally.
Add the tomatoes and season lightly with sea salt and black pepper, then simmer gently over a low heat for 30 minutes, or until thickened and slightly reduced.
When the time's up, remove the chilli, and break up the tomatoes with the back of a spoon. Taste and adjust the seasoning, if needed, then add a tiny swig of red wine vinegar to give it a little twang.
Preheat the oven to 220°C/425°F/gas 7.
Pour the tomato sauce into a 20cm x 30cm roasting tray. Season the fish fillets on both sides with a little salt and pepper, then place on top of the sauce.
Squash the olives, using the base of a jar or something heavy, and remove the stones. Sprinkle into the tray, along with the capers and most of the basil leaves over the fish.
Cook in the oven for around 15 minutes or until the fish is cooked through – check by cutting into the thickest part of one or two of the fillets; they should be pearly white and not transparent.
Scatter over the remaining basil leaves. Lovely served with new potatoes and a green salad.