5 cups fresh or frozen blackberries
3/4 cup sugar
2 tablespoons all-purpose flour
1 tablespoon lemon juice
1 teaspoon grated lemon peel
1 teaspoon vanilla extract
TOPPING:
1 cup all-purpose flour
1/2 teaspoon baking powder
1/2 teaspoon baking soda
2 egg whites
1/2 cup fat-free plain yogurt
2 tablespoons butter or stick margarine, melted
2 tablespoons lemon juice
1 teaspoon vanilla extract
1/2 cup reduced-fat whipped topping