Preheat oven to 350 degrees F. In medium bowl combine flour, sugar, cocoa powder, baking powder, baking soda, and salt. In blender combine water, blueberries, and the egg. Cover and blend until smooth. Add to flour mixture. Whisk until well combined. Pour into greased 8x8x2-inch baking pan.
Bake 30 minutes or until a toothpick inserted in center comes out clean. Cool completely on wire rack. Invert onto serving platter.
In small microwave-safe bowl combine dessert topping and chocolate pieces. Micro-cook, covered, on 50 percent power (medium) 1 minute. Stir until smooth. Let stand 5 minutes. Pour onto cooled cake, spreading evenly.
Cut cake into squares to serve. Top with fresh blueberries. Serve with Blueberry Sauce. Makes 9 servings.
In blender combine dessert topping and blueberries. Cover and blend until smooth.