1 1/2 teaspoons double-acting baking powder
1 cup vanilla yogurt or sour cream
1 teaspoon baking soda
1 stick (1/2 cup) unsalted butter, softened
1 cup granulated sugar
2 large eggs
1 teaspoon vanilla extract
Zest and juice of one lemon
1 1/2 cups fresh or frozen blue berries
1/2 cup all-purpose flour
1/4 cup sugar
In a large bowl cream together the butter and 1 cup of the granulated sugar until the mixture is light and fluffy, add the eggs, 1 at a time, beating well after each addition, and beat in the vanilla and lemon zest. Stir in the flour mixture alternately with the sour cream mixture and stir the batter until it is combined well.
Pour the batter into a buttered 9 X 13 cake pan. Sprinkle blackberries evenly on top.