A staple snack at Christmas markets across Germany, kartoffelpuffer are crisp potato pancakes served with a dollop of tart apple sauce. These make a great snack with a glass of cold beer, or try them with a warming glühwein , just as they would in Germany.
Peel the potatoes and grate them into a bowl. Grate in the onion and add the flour and eggs, stirring well to mix together. Season generously with salt and pepper and stir in the horseradish or mustard, if using. Set aside.
For the apple sauce, peel, core and chop the apples, dropping them into a saucepan as you go. Add 2 tablespoons of water and set over a medium heat, covering with a lid. Allow to cook until soft, about 5–8 minutes, mashing them with a spoon from time to time to help them along. Season to taste with a little sugar, bearing in mind that the sauce is supposed to be quite tart, and spoon into a bowl to cool a little. The sauce can be served warm or made in advance and served cold.
Add 2–3 tablespoons of vegetable oil to a large frying pan and set over a high heat. Once the oil is hot, dollop a few tablespoons of the potato mixture into the pan, flattening them out until around 1cm thick, and allow to fry for 2–3 minutes until crisp and golden. Flip over with a palette knife and fry on the other side. Remove to a plate lined with kitchen paper and keep warm in a low oven (around 110°C/90°C Fan/Gas Mark ¼) while you make the rest. Serve hot with a dollop of apple sauce on top.