For crust, in a medium bowl, combine flour and the 3 tablespoons sugar; cut in butter until mixture is crumbly. Press into bottom of 13x9x2-inch (3-quart rectangular) baking dish. Bake in a 350 degree F oven for 20 to 25 minutes or until golden.
Meanwhile, in a large saucepan, combine raisins, water, and the 3/4 cup sugar. Bring to boiling; reduce heat. Cover and simmer for 10 minutes.
Mix the 1/3 cup sugar, the cornstarch, salt, and spices; set aside.
Stir together egg yolks and sour cream. Gradually stir into sugar mixture until smooth; add to raisin mixture. Cook and stir just until mixture just comes to a boil. Stir in lemon juice; pour over crust.
In a large bowl, combine egg whites and baking powder. Beat with an electric mixer until soft peaks form (tips curl). Gradually add the 1/2 cup sugar, beating until stiff peaks form (tips stand straight). Carefully spread over hot filling.
Bake in a 350 degree F oven for 15 minutes. Cool for 30 minutes. Chill in the refrigerator for at least 4 hours. Cut into squares. Makes 20 to 24 servings.