Butter an 8-inch souffle dish on the inside, and wrap a 6-inch band of double-folded aluminum foil around to form a collar or upward extension of the dish. The collar should rise 3 inches above the lip of the souffle dish, and can be secured with three wraps of cotton string tied in a knot.
In a saucepan melt the butter over medium heat, then slowly stir in the flour, scraping until all is incorporated, making a roux. Reduce heat to the lowest possible, and continue working the mixture with a wooden spoon, removing from the heat before browning occurs, and continuing off and on over low heat for 5 minutes.
Add the hot milk and whisk into the roux, simmering for 3 minutes to achieve a very thick sauce.
Remove from the heat, then add the salt and peppers and stir. Pour this sauce into a large, warmed crockery mixing bowl. Stir in the egg yolks one at a time. Finally, add the salmon flakes, gently blending them into the sauce base.
In a chilled mixing bowl (copper is best), add 1 tablespoon ice water, and then the egg whites. Beat the mixture to stiff peaks. Spoon 2 tablespoons of the egg whites into the salmon mixture and incorporate. Spoon the rest of the egg whites on top of the salmon mixture and carefully fold the two together.
Tip the mixture into the collared bowl. Place in a pre-heated 400°F oven, and immediately reduce the temperature to 375°F. Bake the souffle for 30 to 45 minutes, or until it has puffed 1 or 2 inches above the aluminum collar and is nicely browned. Serve immediately.