1. To make the sauce, heat the butter in a frying pan and gently fry the shallot to soften, without letting it colour. Add the mushrooms and cook until the juices begin to flow. Add the stock and simmer for 2—3 minutes.

2.  Put the cornflour and mustard in a cup and blend with 15 mi/i tbsp water. Stir into the mushroom mixture and bring to a simmer, stirring to thicken. Add the crème fraiche, tarragon, vinegar, salt and cayenne pepper.

3.  For the fish, melt half of the butter in a large, non-stick frying pan. Season the salmon steaks and cook over a moderate heat for 8 minutes, turning once.

4.  Spoon the sauce over each salmon steak and serve with new potatoes
and a green salad.