Peel the apple if necessary, this is not absolutely necessary, and rub it on a coarse grater. Add all other ingredients, mix together and let soak for 5 minutes. If you like, you can also add half a teaspoon of grated lemon zest to the batter.
Bake the batter in a waffle iron until golden brown. Let the finished waffles cool on a rack and dust with a little icing sugar. The batter makes 4 waffles.