1/2 cup unsweetened Dutch-process cocoa powder
1/3 cup plus 1/4 cup sugar
8 large egg whites
1 cup diced cooked beets
3/4 cup chopped walnuts
Preheat oven to 325 degrees F. Lightly coat an 8-inch square metal baking pan with cooking spray. Using a fine sieve, sift cocoa powder and 1/3 cup sugar to remove lumps. Set aside. In a large mixing bowl, using an electric mixer on the highest speed, beat egg whites until soft peaks form. Beat in remaining 1/4 cup sugar until just incorporated. Gently fold in half of the cocoa mixture. Fold in remaining cocoa mixture, then beets and nuts. Transfer batter to prepared pan and smooth the top. Bake 40 to 45 minutes or until top is cracked and slightly puffed and toothpick inserted in the center comes out clean. Remove from oven and cool on wire rack 5 minutes. Run a knife around edge of pan and invert brownies onto a rack. Immediately flip onto a second rack (so brownies are top-up) to cool. Cut into nine bars. Store brownies in a plastic container and refrigerate for up to three days.