Preheat oven to 250 degrees F and preheat waffle iron.
Sift together flour, brown sugar, baking powder, baking soda, salt, and spices.
Whisk egg yolks in a large bowl with buttermilk, pumpkin, and butter until smooth. Whisk in dry ingredients just until combined.
In a mixing bowl with a whisk attachment, whisk the egg whites until they hold soft peaks. Fold them gently into the waffle batter until just combined.
Brush waffle iron lightly with oil or spray with cooking spray (I like to use Pam for Grilling because it's a high temperature formula and holds up better to heat of my waffle iron). Pour or spoon batter into waffle iron, spreading quickly. Cook according to manufacturer’s instructions. When I make waffles, I like to transfer the batter to a pourable measuring cup and pour it onto the waffle iron. I don't even bother spreading the batter because the weight of my waffle iron's lid spreads it nicely.
If serving many people, transfer waffles to rack in oven to keep warm and crisp. Repeat with remaining batter. I just cool my extra waffles on a cooling rack, break up the squares, wrap them in waxed paper, and pack them up in freezer bags. Then they are ready to pop in the toaster from frozen.