- Heat oven to 350 °F.
- Grease 8-inch square pan.
- In small bowl, stir together cocoa, flour and baking powder; set aside.
- In medium bowl, stir together vegetable oil, brown sugar and granulated sugar; stir in beaten egg whites and vanilla.
- Gradually stir in cocoa mixture until blended.
- Pour into prepared pan.
- Bake 15 to 20 minutes or until brownie begins to pull away from side of pan.
- Cool completely in pan on wire rack.
- Just before serving, cut into bars or cut with cookie cutters; sprinkle with powdered sugar, if desired.