Drain the can of salmon and set aside. Beat together the eggs, cream or fromage frais and tarragon. Season lightly. Melt the butter in a non-stick or omelette pan. Pour in the eggs and cook over a moderate heat until the base is set. While the base is setting, preheat a moderate grill. Arrange the canned salmon over the soft top of the omelette. Place the pan under the grill until omelette is set. Loosen the omelette in the pan and carefully fold in half: Slide the omelette onto a serving plate garnished with salad.