Preheat the waffle iron: Preheat your waffle maker according to the manufacturer’s instructions.
Mix the dry ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, salt, and sugar.
1 ½ cups whole wheat flour, 2 teaspoons baking powder, ¼ teaspoon baking soda, 2 tablespoons white sugar, ½ teaspoon salt
Mix the wet ingredients: In another bowl, whisk together the egg, buttermilk, vanilla, and melted butter until smooth.
1 large egg, 1 ½ cups buttermilk, 5 tablespoons butter, 1 teaspoon vanilla extract
Optional step for fluffier waffles: Separate the egg first. Whisk the egg white until soft peaks form, then gently fold it into the batter as the very last step. This gives the waffles a lighter, airier texture.
Combine the batter: Pour the wet ingredients into the dry ingredients and stir gently until just combined. Do not overmix. The batter should still look slightly lumpy. Overmixing develops the gluten and can make the waffles dense instead of fluffy.
Rest the batter: Let the batter sit for 5–10 minutes before cooking. This helps hydrate the whole wheat flour and creates waffles with a softer interior and better texture.
Prepare the waffle iron: Lightly brush the waffle griddle with butter or oil before the first waffle.
Cook the waffles: Add about ¼ cup + 2 tablespoons batter for rectangular waffles like mine, or about ¼ cup batter for smaller irregular waffles. Cook according to your waffle maker instructions until golden brown and crisp outside.