Preheat oven to 350°F (180°C).
In medium bowl combine flour, cocoa, baking powder and salt. In large bowl with mixer at high speed, beat egg and egg whites until foamy. Add 1/2-cup sugar. Beat 1 minute. Add remaining sugar. Beat until slightly thickened. Beat in butter. Gradually blend in dry ingredients.
Place in greased 8-inch (20cm) square baking pan.
Bake 20 to 25 minutes or until edges pull away from sides of pan. (Do not over bake). Cool completely on wire rack. Chill 10 minutes for easier cutting. Cut into 2 x 1-inch (3cm) bars.