In a large bowl, mix together milk, egg yolk, pumpkin, vanilla, oil, and brown sugar. In a separate bowl beat egg white until firm peaks form, set aside. Slowly combine dry ingredients to wet ingredients. Lastly, fold in the egg whites to the batter.
Once the waffle iron is hot, spray with nonstick cooking spray or brush with melted butter.
Pour 1/2 cup to 3/4 cup of batter onto the waffle iron, depending on how large your waffle iron is. Close the top and cook about 2 minutes, or until desired doneness.