An assortment of Martha's favorite cheeses -- Emmental, Comte, Scharfe Maxx, Appenzeller, and Pleasant Ridge -- sets this souffle apart.
Preheat oven to 400 degrees on a conventional oven or 375 degrees in a convection oven.
Butter a 7-inch round 3 3/4-inch high 9-cup souffle dish. Using a piece of parchment paper, form a collar around souffle dish so that it extends 3 1/2 inches above the top of the dish; using kitchen twine, tie to secure. Place on a rimmed baking sheet and set aside.
In a large saucepan, whisk together flour and salt. Gradually whisk in half-and-half and place over medium-high heat, whisking constantly until thick and smooth.
Transfer to a large bowl; scatter butter over top. Butter will melt and prevent a skin from forming on surface. Let cool until lukewarm.
Stir in egg yolks and cheese; set aside.
In the bowl of an electric mixer fitted with the whisk attachment, beat together egg whites and egg white powder until medium to stiff peaks form. Gently fold egg whites into bowl with cheese mixture. Transfer to prepared souffle dish.
Transfer to oven and bake until souffle is risen and set, 40 to 45 minutes. Remove collar and serve immediately.
14 ounces of other hard cheeses may be substituted for those listed.