Put the duck in a shallow dish, sprinkle with the thyme, sherry, salt and pepper and let marinate for about 30 minutes.

Pat the duck dry with kitchen paper and heat a frying pan on a high heat until smoking. Add the duck skin side down and fry without oil on one side only for 5 minutes until deep golden brown. Remove the duck to a plate. Drain off the duck fat and keep to cook potatoes on another occasion. Wipe the pan, heat 1 tablespoon of the oil, add the shallots and fry until pale golden.

Transfer to the plate with the duck.

Heat the remaining oil, add the onions and garlic and fry gently for 5 minutes until softened but not coloured. Increase the heat, add the wine and bring to the boil. Transfer to a shallow ovenproof casserole, add the shallots and duck breasts, skin side up, and the marinade.

Cook in a preheated oven at 220°C (425°F) Gas 7 for 5 - 8 minutes. If you prefer the duck to be more well done, cook for 3-5 minutes longer.

Add the olives and cook for a further 5 minutes. Slice the duck breasts lengthways, then serve with the olive and onion mixture.