Preheat oven to 350. Spray a 13x9 baking pan with cooking spray.
In a medium bowl, combine currants with baking soda and boiling water. Let stand 30 minutes. In a medium size bowl, combine flour, cinnamon, and salt.
In a large bowl, beat together apple sauce, sugar, egg whites, lemon juice, and vanilla with an electric mixer on medium speed until blended. Add flour mixture alternately with currant mixture, beginning and ending with flour.
Mix by hand until flour mixture is combined with currant mixture. Pour batter into prepared pan. Bake 30 to 35 minutes or until center tests done. After it cools, cut into squares and serve.