Preheat your waffle iron to the desired temperature setting.
In a small mixing bowl, whisk together the flour, baking powder, salt, and sugar.
Pour in the milk or buttermilk, add the beaten egg, and melted butter to the dry ingredients. Stir everything together until just combined, taking care not to over-mix. Allow the batter to rest for 2 minutes.
Pour the batter into the preheated waffle iron and cook according to the manufacturer's instructions until the waffle is golden brown and crispy.