Peel and wash the potatoes, then place them in salted water and bring to the boil and simmer for a minute. Drain the water and allow them to cool.
Next shred the potatoes, using a grater, into a large bowl. Heat the butter in a saucepan until it melts then add a little at a time to the shredded potatoes just enough to allow the mixture to bind together and season lightly with salt and pepper. You could add some herbs (maybe some fresh picked thyme or finely chopped rosemary) at this point, if you wanted to.
Form the mixture into rounds either by hand or using a ring mould.
Fry the shaped rosti in a hot pan on both sides until crisp and golden brown.