Using a KitchenAid Stand mixer (or mix by hand), eggs, buttermilk, unsalted butter, vanilla extract, and pumpkin puree for 30 seconds on STIR mode.
In a separate bowl, combine all the dry ingredients, all-purpose flour, pumpkin pie spice, sugar, baking powder, baking soda, and salt.
Add the dry ingredients to the wet ingredients, mix on "STIR" setting for 10 seconds then bump up to speed 2 for an additional 20 seconds. Scrape down the sides of the bowl and mix again for another 5-10 seconds.
Spray the waffle iron with cooking spray, ladle 1 cup batter into waffle iron. Cook for 3 minutes or until golden in color. Repeat until all the batter is used.
Cool Butter - Whenever I make buttermilk waffles. The first thing I will do is melt and begin to cool the butter. If you pour hot butter into the batter with the cold buttermilk, the butter will immediately harden making it difficult to incorporate throughout.
Waffle Irons - Depending on the size of your waffle iron will depend on how much batter you need to place in the waffle iron. I've tested both KitchenAid Waffle Baker and Cuisinart Griddler with Waffle Iron Plates. Both have taken 3 minutes to cook the waffles.
Freeze - You can freeze any leftover waffles. Lay them flat or wrap them between parchment paper, place in a freeze bag, and label with recipe title and date.
Fresh Waffles - Store waffles in an airtight container for up to 5 days in the refrigerator.
Reheating Waffles - Whether the waffles are frozen or fresh simply place a waffle in a toaster oven on low setting. Cook until warm and just crispy.