Bechamel Sauce: Warm up the milk in a sauce pan. In another pan melt the butter and add the flour. Whisk and cook until well mixed and toasted.
Pour the warm milk a little at the time and keep whisking to prevent lumps. Season with salt and pepper and cook for 5 to 7 minutes or until it thickens in a sauce.
Remove form heat and cover with baking paper directly on the sauce, so it won't form the yellowish tough skin. Cool at room temperature.
Salmon Flan: Preheat the oven to 180 degrees C. Grease with butter and sprinkle with breadcrumbs 4 ramekins.
Reserve a few slices of salmon for decoration then diced the remaining salmon.
In a bowl beat the eggs until frothy. Add mustard and cooled bechamel sauce. Stir in the chopped salmon. Divide the mixture in the 4 ramekins, covering by 2/3.
Bake in the preheated oven for 15 to 20 minutes or until golden.
Remove from oven, let slightly cool, then flip on serving plates. Decorate with the reserved sliced salmon, some salad and a drizzle of fresh oil.
You can also bake this flan in a water bath, so they will get even softer and moister. Or with the same ingredients you can make a soufflè: just separate the eggs and beat the whites to stiff peaks before adding to the mixture as very last ingredients. If making a soufflè, bake it in a water bath.