In a large bowl (the batter will double in size), combine all ingredients. Whisk until combined (the batter will be lumpy).
Cover the bowl securely with plastic wrap and let the batter rise in the fridge overnight, or at least 8 hours.
When risen, set the batter on the counter for at least 30 minutes prior to cooking—stirring once.
Preheat the waffle iron and spray with nonstick cooking spray.
Scoop ¹/³cup of the batter into the center of the iron and close the lid.
Bake until golden brown—about 5 minutes. Repeat with the remaining batter.
Serve immediately, or keep in a warm oven until ready to serve. Serve with butter and a generous amount of maple syrup.