Get Ready: Preheat your oven to 200°F (to keep waffles warm) and heat up your Belgian waffle iron to medium.
Combine Dry Ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg, and cloves for about 30 seconds. Make a small well in the center and set it aside.
Whip Egg Whites: In a separate medium bowl, add the egg whites and cream of tartar. Using an electric hand mixer on high speed, whip until soft peaks form. Then, add 2 tablespoons of the granulated sugar and continue whipping until you get medium-stiff, glossy peaks. This step makes your waffles extra fluffy!
Mix Wet Ingredients: In another medium bowl, whisk together the milk, buttermilk, oil, pumpkin puree, vanilla extract, egg yolks, and the remaining 3 tablespoons of granulated sugar until well combined.
Combine & Fold: Slowly pour the wet pumpkin mixture into the dry flour mixture while whisking gently. Mix just until everything is combined – a few lumps are perfectly fine! Then, gently fold in the whipped egg whites. This keeps the batter light and airy.
Cook Your Waffles: Lightly spray your waffle iron with cooking spray. Pour enough batter to fill your iron (about one scant cup for most Belgian irons) and cook according to your waffle iron's instructions until golden brown and crisp.
Keep Warm: Place cooked waffles in the preheated oven to keep them warm while you finish the rest of the batter.
Serve & Enjoy: Serve your delicious pumpkin waffles warm with your favorite syrup or a dollop of whipped cream!