Preheat oven to 350°.

Lightly coat the bottom of a 9×9×2-inch baking pan with nonstick cooking spray, being careful not to coat sides of pan

In a medium saucepan melt butter; remove from heat.

Stir in granulated sugar, water, and vailla.

Stir in flour, cocoa powder, and baking powder until combined.

Stir in chocolate pieces.

Pour batter into prepared pan.

Bake 15 to 18 minutes, or until a wooden toothpick inserted near the center comes out clean.

Cool on a wire rack. Remove from pan. Cut into 16 squares. Sprinkle with powdered sugar if desired.