Preheat the oven to 180C/350F/Gas 4.
Season the herring fillet with salt and freshly ground black pepper and place on a baking tray, skin-side down.
For the tapenade, place all the tapenade ingredients in the bowl of a small food processor and process until smooth.
Spread the tapenade over the herring fillet and place in the oven to cook for 7-8 minutes, or until cooked through.
For the sweet and sour tomatoes, heat the oil in an ovenproof frying pan and fry the tomatoes on all sides. Add the sugar and vinegar and stir. Transfer to the oven to cook for around five minutes.
For the butter sauce, heat a small frying pan, add the white wine and simmer until reduced by half. Stir in the cream and butter and continue to cook over a low heat until the butter has melted.
To serve, spoon the sauce into the centre of a serving plate and lay the fish fillet on top. Spoon the tomatoes around the sides and garnish with a sprig of fresh dill.
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