In a large mixing bowl, whisk together the flour, brown sugar, baking powder, baking soda, salt and cinnamon; set aside
180 g white whole wheat flour, 30 g brown sugar, 12 g baking powder, 3 g baking soda, 3 g salt, 2 g cinnamon
In a medium mixing bowl (or pitcher), whisk together the egg yolks, buttermilk, yogurt and vanilla until well combined.
3 egg yolks, 240 ml buttermilk, 150 g yogurt, 5 ml vanilla
Pour the wet ingredients into the dry ingredients and fold until just combined. Avoid overmixing — a few small lumps are fine.
Stir in the melted, cooled butter. Add the sourdough discard and mix until incorporated.
75 g butter, 120 g sourdough discard
In a small mixing bowl, beat the egg whites to stiff peaks. Stir about 1/3 of the egg whites into the batter to lighten the batter. Gently fold the remaining egg whites into the batter until no white streaks remain. Let the batter rest for about 20 - 60 minutes.
3 egg whites
Preheat your waffle iron. Using a ½ cup scoop (or the amount recommended by your waffle iron manufacturer), portion the batter into the center and gently spread it to cover the grid. Close the iron and cook until the waffle iron indicates it’s done (typically 3-5 minutes depending on your waffle iron).
Transfer cooked waffles to a 180°F oven to keep warm and crisp while you finish the batch. Serve warm with butter and syrup, fresh fruit, powdered sugar, or your favorite toppings.
Notes
The 20-60 minute rest is not strictly required because the chemical leavening agents will provide most of the rise for these waffles - but, if you can spare the time, you will not only get a better depth of flavor, but the yeast will get a chance to wake up a little and add a bit more lift resulting in an even more airy, fluffy interior.