Slowly pour the liquid ingredients into the dry ingredients while gently stirring, and mix just until combined. (Don’t overmix or the waffles will be tough and chewy). The mixture will be a little lumpy (and that’s OK; if you have pockets of flour bigger than a dime, smash them against the side of the bowl to break them apart without having to stir the batter more).
Pour in the melted butter and gently mix with a spoon just until incorporated.
If using an electric griddle or waffle maker, set the heat to 350°F.