Combine in a mixing bowl:
Equal parts (1) seasoned mashed potatoes (leftovers work great!) and (2) sauerkraut
Add finely chopped onion to taste. No salt should be needed if the potatoes were salted.
Mix well. Heat a little oil (your choice what kind) in a frying pan. Meanwhile, use your hands to form the above mixture into small patties. Place in the hot frying pan and cook until browned. Flip and cook on the other side. Repeat with the remaining mixture, adding more oil as needed. There is no need to deep fry them; I just use a little oil in the pan.