Apple Cider Waffles

flour 2 tablespoons sugar 1 teaspoon ground cinnamon 1 teaspoon baking powder 1/2 teaspoon baking soda 1 teaspoon kosher or sea salt 2 eggs, separated 1 cup buttermilk *see note 1 1/4 cup unsalted butter, melted 3/4 cup apple cider