Feather Sponge Cake
["6 egg yolks", "1/2 c. cold water", "1 1/2 c. sugar", "1/2 tsp. vanilla extract", "1/2 tsp. orange or lemon extract", "1 1/2 c. cake flour", "1/4 tsp. salt", "6 egg whites", "3/4 tsp. cream of tartar"]
["Beat egg yolks until thick and lemon-colored.", "Add water and continue beating until very thick.", "Gradually add sugar, then extracts.", "Fold in flour sifted with salt, a little at a time. Beat egg whites until foamy; add cream of tartar and beat until they form moist, glossy peaks.", "Fold into egg yolk mixture.", "Bake in 10-inch ungreased angel-cake pan in slow oven (325\u00b0) for 1 hour.", "Invert pan to cool."]
["egg yolks", "cold water", "sugar", "vanilla extract", "orange", "cake flour", "salt", "egg whites", "cream of tartar"]