75g pack watercress

300ml fish stock

50g butter, cut into small pieces

1 egg yolk

2 tbs oil

2 salmon fillets

100g chestnut mushrooms, quartered

1 garlic clove, thinly sliced

salt and pepper

Put a quarter of the watercress in a food processor or blender and whizz until finely chopped. Set aside. In a small pan, bring the stock to the boil and keep boiling until reduced to four tbs. Lower heat and add the butter a few pieces at a time, swirling to combine. When all the butter has been used, whisk in the egg yolk. The mixture should thicken after 1 minute. Remove from the heat and stir in the chopped watercress, season if necessary. Set aside. 

Heat half the oil in a frying pan and fry the salmon for 2-3 mins each side. Remove and keep warm.

Heat remaining oil and fry the mushrooms and garlic for 1 minute, then add the remaining watercress for 20 secs until just wilted. Warm the sauce on the lowest heat. Spoon the watercress mixture on to plates, top with the salmon and spoon over the sauce.