Gently heat the crème fraiche in a small saucepan until just beginning to boil. Remove the pan from the heat and stir in half the tarragon. Leave the herb cream to infuse while cooking the fish.

Heat the butter and oil in a frying pan and fry the salmon fillets for 3-5 minutes on each side. Remove from the pan and keep warm.

Add the garlic and fry for a further 1 minute, then pour in the wine and let it bubble until reduced to about 15 ml/1 tbsp.

Meanwhile, strip the leaves off the watercress stalks and chop finely. Discard any damage leaves. (Save the watercress stalks for soups, if you wish.)

Strain the herb cream into the pan and cook for a few minutes, stirring until the sauce has thickened. Stir in the remaining tarragon and watercress, then cook for a few minutes, until wilted but still bright green.

Season to taste with salt and pepper and serve at once, spooned over the salmon. The dish can be accompanied by a mixed lettuce salad if you wish.