Try other seasonal fruits, such as apples or pears, in this moist and tender cake. Use just enough sliced, peeled fruit to cover the entire surface of the cake batter, and then top with the cinnamon-flavored streusel.
Preheat oven to 350 degrees F. Grease a 13x9x2-inch baking pan; set aside. For topping, in a small bowl stir together brown sugar, nuts, and cinnamon. In another small bowl stir together sour cream and baking soda.
In a large bowl combine granulated sugar and butter. Beat with an electric mixer on medium speed until light and fluffy. Add eggs and vanilla; beat until combined. Add flour and baking powder; beat until combined. Beat in sour cream mixture.
Pour half of the batter into the prepared pan, spreading evenly. Sprinkle with blueberries and half of the topping. Carefully pour remaining batter over layers in pan, spreading evenly. Sprinkle with remaining topping.
Bake for 35 to 40 minutes or until a toothpick inserted near the center comes out clean. Drizzle with Powdered Sugar Icing. Serve warm or cool completely.
Powdered Sugar Icing
In a small bowl stir together powdered sugar, 2 teaspoons milk, and the vanilla. Stir in enough additional milk, 1 teaspoon at a time, to make icing a drizzling consistency.