Add the dry ingredients in a large mixing bowl: flour, sugar, baking powder, baking soda, and salt. Stir with a wooden spoon or large whisk.
Pour all the wet ingredients on top: buttermilk, melted butter, eggs, and vanilla. Stir until the batter is completely combined. Be careful not to over-mix, it is normal for the batter to have some clumps.
Spay the iron with nonstick spray or coat it with a bit of butter.
Scoop about 1/2 cup of batter for a single waffle iron or 1 cup for a large multiple waffle iron. Spread it out slightly while you pour it into the iron to ensure an even waffle.
Close the iron and allow it to cook per the iron manufacturer's instructions.
Remove and serve immediately, or cover until all the waffles are baked.