Preheat the oven to 200°F. Place a wire rack on a large baking sheet and set aside.
In a large bowl, whisk together the gluten-free flour, sugar, baking powder and salt.
In a separate bowl, lightly beat the egg yolks, then add the milk and oil. Mix well to combine.
Add the wet ingredients to the dry ingredients and stir until just combined.
In another bowl, beat the egg whites with an electric mixer until fluffy and stiff peaks begin to form.
Gently fold the egg whites into the batter using a rubber spatula.
Preheat the waffle iron. When the waffle iron is hot, lightly spray the inside with cooking spray, then scoop in the batter. Cook until golden brown, according to the waffle maker’s instructions.
Serve immediately or keep warm on the wire rack-lined baking sheet in the warm oven until ready to serve.