Meat: Pour the water, onion, carrot, bay leaf, peppercorns and white wine into a tall saucepan – there should be enough liquid to just cover the meat later on. Bring to the boil, season with salt, reduce the heat and add the meat. Poach just below simmering point for about 1 hour, until the meat reaches a core temperature of 56–58 °C (133–136 °F). Remove the pan from the heat and leave the meat to cool completely in the stock. Set aside about 6 tbsp of the stock.

Tuna sauce: To make the mayonnaise, whisk the egg in a tall jug using a hand mixer. Add the oil while stirring constantly, drop by drop at first, then gradually in a thin stream, until a thick mayonnaise forms. Stir in the lemon juice, mustard and salt.

Drain the tuna, capers and anchovy fillets, chop them finely and add to the mayonnaise. Blend with the reserved poaching stock. Season the sauce with a little lemon zest and pepper.

Carve the cooled meat very thinly across the grain, arrange on plates and spread the sauce evenly over the top. Garnish with caper berries if desired.