- Place the stock, shallot, lemon slice, bay leaf and peppercorns in a pan wide enough to hold the fillets in a single layer. Bring to the boil, then remove from the heat and set aside to infuse while you make the sauce.
- Melt the butter in a small saucepan. Pour off the clear golden liquid into a small bowl, discarding the milky sediment, and set aside to cool slightly.
- Put the orange juice, vinegar, peppercorns and 1 tbsp water in a small saucepan and boil for 2 minutes or until reduced by half. Transfer to the top of a double boiler or a heatproof bowl set over a saucepan of simmering water. The base of the pan or bowl should not touch the water.
- Whisk in the egg yolks and continue whisking for 4–5 minutes or until the mixture thickens and becomes pale. Gradually whisk in the melted butter, drop by drop. Continue whisking after all the butter has been incorporated, until the sauce is thick enough to hold a ribbon trail on the surface when the whisk is lifted – this will take 4–5 minutes.
- If at any point the sauce begins to curdle, immediately remove it from the heat, add an ice cube and whisk briskly until it comes together again. Remove the ice cube, return to the heat and continue whisking in the butter.
- Stir in the lemon juice and orange zest and season with salt and pepper to taste. Remove the saucepan or double boiler from the heat. Stir in the tomatoes, then cover and set aside while you poach the fish.
- Strain the cooled fish stock and return it to the pan. Add the fish fillets – the liquid should just cover the fillets; if there is too much, spoon it off and reserve to use in fish soups. Slowly increase the heat so the stock just simmers but doesn't boil, and poach the fish fillets for about 5 minutes, depending on the thickness, until they will flake easily.
- Remove the fillets with a fish slice, gently shaking off any excess liquid, and set on warmed plates. Spoon over the sauce, garnish with tarragon sprigs and serve.
Some more ideas
Turbot is an expensive fish. For a more economical version, you can use 8 skinned sole fillets, about 70 g (2¼ oz) each, poaching them as in the main recipe. * Instead of the sauce maltaise, serve the fish with a fresh orange and tomato salsa. Halve and finely chop 200 g (7 oz) mixed red and yellow cherry tomatoes. Peel and segment 2 oranges, and chop the segments. Toss the oranges and tomatoes together. Season with salt and pepper to taste, and sprinkle over 2 tbsp finely chopped fresh herbs, such as tarragon, parsley and chives. Stir gently, then cover and chill until required. * The poaching liquid can be cooled and stored in the fridge for up to 1 day to use as the base of a fish soup.
Turbot is an excellent source of niacin, needed to release energy from carbohydrate foods. * Tomatoes contain lycopene, a valuable antioxidant. Recent studies suggest that lycopene may help to protect against bladder and pancreatic cancers.
Each serving provides
B1, B12, niacin * A * B6, C, E, calcium, iron, potassium