1 cup all purpose flour 1 cup whole wheat flour (I used King Arthur) ½ cup unsweetened cocoa powder ½ tsp baking powder ½ tsp salt 1 tsp baking soda ½ cup vegetable oil 1¼ cup dark brown sugar packed 2 eggs ¾ cup spinach puree (I used frozen spinach and pureed in my food processor) 2 tsp pure vanilla extract ½ cup milk nonstick cooking spray