Peel the potatoes then grate them with a coarse cheese grater. Squeeze out any excess water then wrap them in a clean tea towel. Squeeze again to remove the leftover moisture.
Season with salt & pepper, toss well, then divide them into four equal portions.
Heat two Tbsps of duck fat or oil in a large frying pan over a medium heat.
Place a metal or silicon ring inside the frying pan and add one portion of the grated potato. Using the back of a spoon, gently push down to flatten the potatoes evenly in the ring.
Remove the ring and repeat with the remaining potato until you have four patties.
Cook the patties for 3-4 minutes on both sides, or until golden-brown, adding more oil /fat if required. Remove them to a plate, lined with kitchen paper.
Serve warm.