Separate 5 eggs. Beat whites until very stiff. Add 2 T. sugar, 1 T vanilla,
Move the beaten egg whites gently to the side of the bowl. Combine the yolks, 1 T. flour and a little lemon zest in the same bowl, and carefully add to the white with metal whisk.
Melt about 1-2 T. butter in a 9x15 Pyrex dish or other oven-proof glass or ceramic dish. Add 1 T. rum (optional) and preheat this is 375 oven.
Make 3 heaping mounds of the egg mass in this dish and bake at 375 for 12 minutes. Sprinkle with powdered sugar and serve immediately!
This is a famous dessert, served only in the finest and most traditional of restaurants in Salzburg, Austria.