Put the egg whites and the sugar in a large glass bowl. Whip them softly until the sugar is disolved. Then, heat some water in a pot that is slightly smaller than the salad bowl. Place the salad bowl on top of the pot and make sure that the water level is just below but not touching the bottom of the bowl.
Slowly bring the water to a boil. Whip the egg whites faster and faster just until the mixture has a uniform texture.
Remove the salad bowl from the pot and continue to whip the eggs until they are completely cooled. You will know your egg whites are ready when you can remove the beater and they don't refill the hole you left behind. If you pick up the bowl and turn it on it's side, they won't even move. (Be careful checking them, if they DO move, do NOT tip the bowl! lol)
Gently fold the flour into the mixture. Fold the cooled melted butter into the egg white mixture.
Butter a cake mold and pour in the batter.
Preheat the oven to just under 300°F (150°C)
Bake the cake for 25 minutes or until lightly browned and set in the middle.
Remove the cake from the pan by placing a wire grill on top of the cake, flipping the grill and pan over and then tapping against a counter or table until the cake comes out.
Allow to cool. Decorate by cutting a shape out of cardboard, placing it in the middle of your cake and then sifting powdered sugar on top. Gently remove the cardboard template and you'll have a beautifully presented, delicious cake.