1. Boil potatoes in their skins until just cooked. Peel and grate coarsely.
2. Melt the butter in a heavy-based frying pan.
3. Add the greated potatoes and sprinkle with salt and pepper.
4. Fry over a moderate heat for about 15 minutes turning as it browns.
5. Just before the end of the cooking time, press down on the potato to shape it in the pan to make sure the pancake is formed properly.
6. Serve, turned upside down, on a large dish.
Try adding bacon pieces - but make sure the bacon is cooked before serving the rosti - I often partially fry the bacon first and then slice into little pieces and add to the pan half way through the cooking process. Try adding some fresh herbs or even chili for a bit of "zing". Onions are also great as well as cheese or even apples for a fruity flavor.