Preheat your waffle iron according to the manufacturer's instructions.

In a medium bowl, whisk together the all-purpose flour, kosher salt, sugar, baking powder, and baking soda. Set the dry mixture aside.

In a 2-cup measuring cup or small bowl, whisk together the buttermilk, large egg, melted butter, and vanilla extract until combined. (If the butter is not yet melted, melt it and let it cool slightly before mixing.)

Pour the wet mixture into the dry ingredients and stir gently with a spatula or whisk until just combined. A few small lumps are fine—do not overmix.

Lightly brush or wipe a little of the melted butter onto the preheated waffle iron grids (use part of the measured melted butter) to prevent sticking.

Pour the appropriate amount of batter onto the center of the waffle iron (follow your waffle iron's portion guidance), close the lid, and cook until the waffle is golden brown and steam has mostly stopped—following your waffle iron’s recommended cook time.

Transfer cooked waffles to a wire rack to keep them crisp while you finish the remaining batter. Serve immediately with your favorite syrup and toppings.