Preheat a waffle iron according to manufacturer's instructions. Spray waffle iron with non-stick cooking spray or brush with oil.
Whisk flour, baking powder, baking soda, and salt together in a bowl.
Beat eggs in a large bowl until light and fluffy. Stir flour mixture into eggs, one third at a time, alternating with buttermilk, until just combined; stir in butter.
Pour batter into preheated waffle iron; cook until golden brown, about 3 minutes.
