Cost per Serving:
1. Make topping: Combine all ingredients in a bowl. Use fingertips to blend until mixture resembles large peas. Refrigerate.
2. Preheat oven to 350°F. Coat a 9-inch round cake pan with cooking spray. Cut a 9-inch circle of parchment; place in pan. Mist with cooking spray.
3. Make cake: In a small bowl, combine flour, baking powder, baking soda and salt. In a separate bowl, beat sour cream, butter and sugar until light and fluffy. Add eggs and egg white. Beat until frothy, about 3 minutes. Blend in vanilla and yogurt until smooth. Stir in flour mixture until just combined. Fold in berries. Spread batter evenly in pan. Sprinkle with topping.
4. Bake cake until a toothpick inserted into center comes out clean, 50 to 55 minutes. Cool on a wire rack for 15 minutes before turning out of pan. Peel off parchment and turn cake right-side up on rack to cool. Cut into wedges and serve.