Whisk flour, sugar, baking powder, baking soda, and salt together in a bowl until evenly combined.
Whisk buttermilk and melted butter together in a separate bowl; whisk in eggs. Stir buttermilk mixture into flour mixture until just combined and batter is slightly lumpy; stir in vanilla extract.
Preheat a waffle iron according to manufacturer's instructions.
To cook each waffle, pour enough batter into the preheated waffle iron to reach 1/2 inch from the edge. Cook according to manufacturer's instructions.