Preheat your waffle iron. A hot iron is key for crisp edges. Set it to medium-high if adjustable.
Blend the dry ingredients. Add oats, baking powder, cornstarch, cinnamon, and salt to a blender. Pulse to make a fine flour.
Add the wet ingredients. Add cottage cheese, eggs, vanilla, and sweetener (if using).
Blend until smooth, about 20–30 seconds.
Adjust the batter. Add milk a little at a time until the batter is thick but pourable. It should ribbon off a spoon, not clump.
Rest briefly. Let the batter sit for 3–5 minutes so the oats hydrate. It will thicken slightly; add a splash more milk if needed.
Prep the iron. Lightly grease with butter or spray to prevent sticking.
Cook the waffles. Pour batter into the center and spread to the edges.
Close the lid and cook until deeply golden and crisp, usually 3–5 minutes depending on your iron.
Finish on a rack. Transfer cooked waffles to a wire rack to keep them crisp. Avoid stacking while hot.
Serve warm. Top with berries and yogurt, a fried egg and hot sauce, or a drizzle of maple syrup.