In a large bowl, mix together the flour, brown sugar, baking powder, pumpkin pie spice and salt. If using salted butter, you can omit the salt.
In a second bowl, whisk together the egg yolks, pumpkin, vanilla and milk.
Before you combine the two mixtures, beat the egg whites to soft peaks.
Once your egg whites are beaten, fold the pumpkin mixture into the flour mixture and stir until fully mixed, then stir in the melted butter. Lastly, fold in your soft-peaked egg whites.
Heat waffle maker as per manufacturer directions and. Brush lightly with high smoking point oil like sunflower or grapeseed. If you are using a cast iron waffle maker or something that does not have a nonstick coating, brush before preheating.
Using a generous third cup, spoon batter into waffle maker and use technique from manufacturer to make the waffles. I've noticed with my waffle maker, the brownest setting works best for this recipe because their moist pumpkin consistency takes a little longer to cook through. They need to be completely cooked through so they won't stick.
Notes
If you have some butterscotch morsels around, throw in a handful.