1Preheat oven to 325. Grease 9 x 13 pan. Set aside.
Beat egg whites until stiff. Set aside.
Beat egg yolk and sugar until light. Add water and melted butter. Gradually add flour. Mix well. Then add the lukewarm milk. Mix well.
2Fold one third of egg whites into egg yolk mixture. Fold until well incorporated. Fold in remaining egg whites, one third at a time. I had to use my whisk and gently break up some of the egg whites. Batter will be thin.
3Pour into greased pan. Bake at 325 for 60-70 minutes or until golden brown. After 60 minutes, mine kind of jiggled in the middle, so I did another ten minutes. Dust with powdered sugar if desired.