Prep the apples: Peel and finely dice them into small cubes (about 1/4 inch). Toss with brown sugar, lemon juice, and a pinch of cinnamon.
Set aside so they release a little juice and soften slightly.
Heat the waffle maker: Preheat to medium or medium-high. Lightly oil or butter the plates. A hot, greased surface helps those caramelized edges form.
Mix dry ingredients: In a large bowl, whisk flour, granulated sugar, baking powder, baking soda, salt, cinnamon, and nutmeg until evenly combined.
Mix wet ingredients: In another bowl, whisk eggs, buttermilk, apple cider, melted butter, and vanilla until smooth.
Combine gently: Pour wet into dry and stir with a spatula just until the flour disappears.
The batter should be thick and a bit lumpy. Do not overmix.
Fold in apples: Stir the diced apples and any juices into the batter. If the batter seems too thick, add 1–2 tablespoons more cider or milk.
Cook the waffle donuts: Spoon batter onto the waffle iron, leaving a little space for spread.
Aim for 1/3–1/2 cup per waffle, depending on your iron. Close and cook until deep golden with crisp edges, usually 3–5 minutes. Resist opening too early.
Encourage caramelization: If your iron runs cooler, let the waffles cook an extra 30–60 seconds.
The sugar from the apples and batter should form browned, lacy edges.
Cool on a rack: Move finished waffles to a wire rack so steam escapes and the edges stay crisp. Keep them warm in a low oven (200°F/95°C) if making a big batch.
Make the glaze: Whisk powdered sugar, milk or cider, vanilla, and a pinch of salt until smooth and pourable. Adjust with more liquid or sugar as needed.
Finish and serve: Dip warm waffles in glaze, drizzle over the top, or dust with cinnamon sugar for a lighter finish.
Serve warm for peak crispness.