Begin heating your waffle iron, because that needs to be good and hot to ensure a nice crisp exterior.
In a small bowl, whisk or beat egg whites until soft peaks form and set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda and salt, set aside.
In another medium bowl, whisk the eggs and dark brown sugar together, then gradually whisk in the buttermilk and vanilla. Lastly, whisk the melted butter in.
Immediately combine the buttermilk and flour mixtures, stirring just until incorporated, then stir in the pecans
Gently fold in the egg whites. The batter will be a little lumpy, and quite thick.
Cook waffles according to your waffle iron instructions, and serve immediately with melted butter, warmed maple syrup and more toasted pecans.
Makes 4 large Belgian style waffles, or around 8 regular sized square waffles.
Notes
Once mixed, the batter won't store well. The cooked waffles will keep nicely in the fridge or freezer though. Wrap tightly and re-heat in the toaster.