In a large bowl, combine pumpkin puree, egg yolks, brown sugar, milk, oil, pumpkin pie spice, vanilla, and whisk until smooth.

In another large bowl, whisk together flour, baking powder, salt, and optional cream of tartar.

Add dry ingredients to wet mixture and stir gently until just combined.

Preheat waffle iron and spray with non-stick cooking spray.

In a separate bowl, beat egg whites until stiff peaks form. Gently fold egg whites into batter.

Pour batter onto waffle iron, filling the desired amount, and cook until golden and crisp, about 4 minutes.

Repeat with remaining batter, re-spraying waffle iron as needed.

Serve waffles immediately with butter, maple syrup, or toppings of choice.