Preheat a waffle iron.
In a medium mixing bowl, combine the flour, salt, baking soda, and cornmeal. Set aside.
In a separate mixing bowl, whisk together the buttermilk, egg yolk, and melted butter. Set aside.
Add the egg white to the bowl of a stand mixer. Whip on medium-low speed until foamy, then increase the speed to medium-high until stiff peaks form, about 4 to 5 minutes. Set aside.
Slowly add the buttermilk mixture to the dry ingredients while gently stirring. Once the ingredients have been combined, gently fold in the egg whites.
Spray the preheated waffle iron with cooking spray. Add an appropriate amount of batter to the waffle iron, following the manufacturer's instructions (for my waffle iron, I add half of the batter). Cook the waffle until golden brown, about 4 to 5 minutes.
Place the waffles on a rimmed baking sheet and cover with a clean kitchen towel to keep warm.