Oil and preheat the waffle iron.Whisk brown sugar and cornstarch in a large bowl. Then whisk in remaining dry ingredients.Next, whisk together pumpkin, milk, egg yolks, and melted butter.Add pumpkin mixture to dry ingredients and mix until combined.Whip egg whites until stiff, then fold into batter. (Note: Harry skips this step when he makes the waffles and they turn out fine. He just mixes the whole eggs in with the pumpkin in step 3.)Pour the batter onto your preheated waffle iron and cook. We use a square waffle iron (that doubles as a griddle and panini press!!), but you can make these with a Belgian waffle iron as well.Serve with butter and maple syrup or whipped cream with sprinkle of cinnamon if you want to get fancy.