Soak walnuts in 3 tablespoons apple juice concentrate. Sift baking powder and cocoa into bowl with flour and make a well. Measure 1.3333333333333 cups apple juice concentrate, oil, egg white and banana into measuring cup and add= all at once to dry ingredients and mix. Spread in 13 x 23 cm pan sprayed with nonstick spray. Sprinkle with walnuts on batter evenly and smooth nuts= into batter with back of spoon. Bake at 180ºC or 30 minutes. Cover when slightly warm. Cut in 24 servings and store in freezer to keep fresh.= Yield 24 brownies.