Oil bottom of 8 or 23 cm springform pan. Melt chocolate and butter ( I did this in a saucepan, although the original recipe calls for it being done in a 200-degree oven.). Add flour, sugar, and water; blend well. Add egg yolks one at a time, beating well after each addition. In a separate bowl ( a metal one!) beat egg whites until stiff. Fold gently into chocolate mixture. Turn into prepared pan and bake for 15 minutes in middle of 425 degree oven (I found that in the 23 cm pan, I needed to extend this to 25 minutes for it to be completely cooked.). Let cake cool completely. Sift or sprinkle powdered sugar over top of cooled cake.