Preheat oven to 250 degrees F. Set metal cooling rack over baking sheet. Set aside.
In a large bowl, whisk together flour, sugar, baking powder, salt, cinnamon, and nutmeg. In another bowl, whisk together well shaken buttermilk, melted butter, oil, and egg yolks until smooth.
Slowly add wet ingredients to dry ingredients in two additions. Use a spatula to combine ingredients together until just combined. The batter will be a little lumpy.
In a clean bowl, whip egg whites to stiff peaks. Add egg whites to batter in three additions. Fold gently to combine. The batter will loosen up as you add egg whites.
Allow batter to rest at room temperature for 5 minutes while you heat waffle iron or waffle maker. Waffle iron temperature or setting with vary based on your machine.*
I use this stovetop waffle iron. Once waffle iron hot, lightly brush the top and bottom of iron with fat of choice (clarified butter, melted butter, or oil). Scoop 1 cup of batter into waffle iron. Cook for 2 minutes on each side over medium-high heat until crisp and golden brown. If needed, cook for another 30-45 seconds on each side.
Transfer cooked waffles to prepared rack and keep warm in preheated oven while you cook remaining batter.
Serve waffles immediately with cranberry maple syrup and salted butter.