Chop 1 large Spanish onion and cook in 1 dl (3½ fl oz or ½ U.S. cup) olive oil until a golden colour. Add 500 g (1 lb 2 oz) skinned and deseeded red pimentos and allow to cook together for 15–20 minutes.
Add 3 dl (½ pt or 1¼ U.S. cups) good quality vinegar and reduce by half; season with salt and pepper then add a touch of garlic, 2½ dl (9 fl oz or 1⅛ U.S. cups) tomato purée, and 100 g 3½ oz) sultanas.
Cover with a lid and cook very gently for 1½ hours. Serve cold.