Place flour m saucepan, and add milk gradually while stirring to a smooth paste. Stir over medium heat until sauce thickens. Stir in cheese and seasonings. When cheese is melted, remove from heat. Beat in egg yolks, one at a time. Fold mixture into stiffly beaten egg whites. Bake in ungreased 2-quart casserole in moderately hot oven (425 F.) 25 minutes. Lower heat during last minutes of baking if necessary. Yield: 8 servings.