Preheat oven to 325º F.
In large bowl, combine grated cheese and chilies. Turn into a well-buttered, shallow quartcasserole or Pyrex dish (12″x8″x2″).
Beat egg whites until stiff peaks form.
Combine egg yolks, milk, flour, salt and pepper. Mix until well blended.
Gently fold beaten whites into egg yolk mixture.
Pour egg mixture over cheese mixture in casserole, and, using a fork, “ooze” itthrough the cheese.
Bake 30 minutes; remove from oven and arrange sliced tomatoes, overlapping, around edge ofcasserole.
Bake 30 minutes longer, or until a silver knife inserted in center comes out clean.Garnish with a sprinkling of chopped chilies, if desired.