2/3 cup unsweetened baking cocoa
1/3 cup all-purpose flour
1/2 tsp baking powder
1/8 tsp salt
1/3 cup canola oil
1/3 cup granulated sugar
1/3 cup packed light brown sugar
4 egg whites, lightly beaten
2 tsps vanilla extract
1/2 cup finely chopped walnuts
1/4 cup mini chocolate chips
1/2 cup miniature marshmallows
Preheat oven to 350 degrees.
Line an 8-inch square baking pan with nonstick foil (or lightly spray regular foil with nonstick cooking spray), leaving edges hanging over the pan for handles.
In a medium bowl combine the cocoa, flour, baking powder, and salt; set aside.
In a large bowl whisk together the oil, sugars, egg whites, and vanilla; stir in the cocoa mixture. Spoon batter evenly into the prepared pan. Sprinkle the walnuts evenly over the batter.
Bake at 350 degrees for 25 minutes. Scatter the chocolate chips and marshmallows over the top. Bake another 5 minutes.
Remove from oven and cool completely on a wire rack.
To slice, coat a sharp knife with cooking spray and cut with a rocking motion into 25 squares.