Separate eggs and put whites in refrigerator.
Beat together egg yolks, cornstarch, powdered milk, water, salt, sugar and lemon rind.
Beat whites until very stiff and fold them into the yolk mixture.
Melt butter in a medium hot 9" skillet, and rotate to coat the sides of the skillet.
If you are including the Granny Smith apple, peel and slice the apple into 1/2" slices, and arrange them in the skillet. Allow the apple to cook for about three or four minutes.
Pour the batter into the hot skillet and spread evenly with a spatula Bake at 425º for 12 minutes (or top is golden brown). Serve at once, slathered in butter, sprinkled with lemon juice and cinnamon sugar.
2 servings