Preheat oven to 325 °F. Grease two 8-inch round cake pans (or one jelly roll pan) and line with wax paper, cut to fit.
Beat egg yolks with lemon juice, cold water and vanilla until thick and pale.
Gradually add 3/4 cup of the sugar and blend well, set aside.
Beat egg whites separately until foamy. Add salt and continue beating until soft peaks form.
Gradually add the remaining 1/4 cup sugar and beat until stiff but not dry.
Gently stir a fourth of he whites into yolk mixture.
Spoon remaining whites into yolk mixture, then sift flour and baking powder on top.
Carefully fold until blended.
Spoon into prepared pans and bake for 15 minutes (for round cake pans) or 12 minutes (for jelly roll pan) or just until toothpick inserted in center of cake comes out clean.