For the halibut, heat the oil in a frying pan.
Dredge the halibut in the seasoned flour, shaking off any excess and fry for 4-5 minutes on each side; then add the butter to the pan.
Meanwhile, for the salad, mix the mayonnaise, lemon zest and juice and truffle oil in a bowl until well combined. Season, to taste, with salt and freshly ground black pepper.
Stir in the potatoes, smoked salmon, tarragon and red onion.
To serve, place a halibut steak onto each of four serving plates and spoon the salad alongside. Serve with the rocket.
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