Preheat your waffle iron according to the manufacturer's instructions. Preheat your oven to 200°F to keep the waffles warm.
In a medium bowl, whisk together the flour, arrowroot powder, baking powder, salt, and sugar.
In a separate bowl, beat the egg yolk, milk, vanilla extract, and melted butter until well combined.
Pour the wet ingredients into the dry ingredients and whisk just until incorporated. Do not overmix.
Using an electric mixer, beat the egg white until soft peaks form.
Gently fold the whipped egg white into the batter, being careful not to deflate it.
Cook the waffles according to your waffle maker's instructions until golden brown and crisp.
Place the cooked waffles directly on the oven racks to keep warm while you finish the remaining batter.
Serve immediately with butter, maple syrup, fresh berries, whipped cream, or your favorite toppings.