Preheat the oven to 350ºF.
Make the waffle batter: In a large bowl, sift flour, baking powder, 1 tablespoon sugar and salt to combine. In a small bowl, vigorously whisk the egg yolks until smooth then add the brown sugar, milk, oil, lemon extract and lemon zest. Whisk until brown sugar is dissolved.
Make a well in the center of the dry ingredients. Pour in the liquid ingredients and gently stir the batter with a wooden spoon, until just combined. (You can use a hand beater or a stand mixer on low speed, as well.) Be careful not to overmix the batter. In a very clean bowl, whisk the egg whites until foamy. Add the remaining tablespoon of sugar and beat until soft peaks form. Gently fold the whites into the batter.