In a medium bowl, whisk together the flour, brown sugar, baking powder, baking soda, salt, cinnamon, nutmeg, ginger, and allspice. Set aside.
In another medium bowl, combine the milk, pureed sweet potato, egg yolks, and melted butter. Whisk together until everything is combined.
Add the wet ingredients to the dry, and mix until things are just combined. Set aside.
In a small bowl, whip the egg whites until stiff peaks form. You can do this by hand, but I recommend using an electric hand mixer. Fold the stiff egg whites into the batter.
Prepare the waffles according to your waffle maker’s directions.
Top the waffles with candied pecans, butter, and maple syrup.