Preheat the waffle iron: Let it heat fully on a medium-high setting. A hot iron is key for crisp edges.
Whisk the wet ingredients: In a bowl, combine Greek yogurt, eggs, oil, vanilla, and milk. Whisk until smooth.
Mix the dry ingredients: In a separate bowl, whisk flour, cornstarch, baking powder, baking soda, salt, and sugar.
If using protein powder, whisk it in now.
Combine gently: Add the dry mix to the wet. Stir with a spatula until just combined. The batter should be thick but spoonable.
If it’s too thick, add 1–2 tablespoons more milk.
Rest the batter: Let it sit for 5 minutes. This hydrates the flour and helps the waffles rise and crisp.
Grease the iron: Lightly spray or brush with oil. Avoid heavy greasing, which can soften the crust.
Cook the waffles: Add enough batter to cover the waffle grid without overfilling.
Close and cook until deep golden and crisp, usually 3–5 minutes depending on your machine.
Keep them crisp: Place finished waffles on a wire rack, not a plate. This prevents steam from softening the edges.
Serve hot: Top with berries, a drizzle of maple syrup, peanut butter, or a dollop of extra yogurt.