I use organic ingredients whenever possible, but this cake can also be made with regular supermarket ingredients. Its light as air, low in fat and simple to make. The trick is to prepare all the ingredients in advance. Separating egg whites is easy if you drop the cracked egg in your hand, and allow the whites to run through fingers. Then let whites come to room temperature so they reach their fullest volume. For a truly decadent experience, serve with strawberries and lightly sweetened whipped cream or hot chocolate fudge sauce and ice cream.
Preheat oven to 350°F. On sheet of waxed paper, sift 1/4 cup of sugar with flour and salt three times.
In large grease-free bowl, using an electric mixer at medium-high speed, beat egg whites until frothy. Add lemon juice and beat until soft peaks form. Evenly sprinkle remaining 1 cup sugar over whites, 1/4 cup at a time, and beat at medium speed 1 to 2 minutes. Sift 1/4 cup of flour mixture over whites and gently fold in using a rubber spatula. Add vanilla and orange peel. Alternately fold in remaining flour mixture and grated chocolate until well blended. (Be sure to fold gently to avoid deflating egg whites.)
Scrape batter into ungreased 10-inch angel food or tube pan. Bake until cake is lightly browned and knife inserted near center comes out clean, 40 to 45 minutes. Remove pan from oven and invert onto feet or over neck of a bottle. Let cool 30 to 45 minutes. Run knife around edges of pan and center of tube to remove.