Summer Berry Cake

Name: Summer Berry Cake
Ingredients: CAKE; 2 cups all-purpose flour; 2 1/2 teaspoons baking powder; 1/4 teaspoon salt; 6 tablespoons trans-free margarine or butter, softened; 1/2 cup granulated sugar; 1 egg; 1 egg white; 3/4 cup fat-free vanilla yogurt; 2 tablespoons fat-free vanilla yogurt; 1 cup fresh strawberries, hulled and sliced; 1 cup fresh blueberries; TOPPING:; 1/4 cup trans-free margarine or butter, softened; 1/3 cup packed brown sugar; 1/2 cup all-purpose flour; 3/4 teaspoon ground cinnamon; Confectioners' sugar (optional)