Preheat the waffle maker.
On the next morning, melt the butter first and let it cool.
Add the pumpkin puree, brown sugar, and dry ingredients. Then, mix well.
Separate the eggs. Add the egg yolks to the batter and place the egg whites in a separate bowl to whip them until they become white with soft peaks.
Once the melted butter has cooled to just warm (less than 90 degrees F), slowly add the butter to the batter and mix until completely combined.
Finally, fold in the whipped egg whites.