• Grate the onion and potato by hand or with a food processor and place in a sieve over a bowl to catch the drips. Sprinkle with salt. Use the back of a spoon to squeeze as much liquid out as possible and then tip the onion and potato mixture into a clean tea towel. Roll up the tea towel and twist the ends firmly to extract as much of the juice as possible over the bowl.
  

• Pour away the liquid and you should find a layer of white potato starch at the bottom of the bowl add the potato mixture back into the bowl and mix gently, season then add 3/4 of the beaten egg and a tablespoon of the potato flour. Mix again. Allow the mixture to firm up for five minutes and check again, If too wet add some more potato flour and if too dry add the rest of the egg.
  

• Heat about 2cm oil in a shallow frying pan on a medium heat until shimmering. Take a couple of teaspoons of mixture and shape into a small flat cake. Fry until golden, check the seasoning and adjust if required.
  

• Fry the remaining mixture in batches. Serve at room temperature topped with sour cream, smoked salmon and some dill fronds or snipped chives.

 Louis Mann / The Butcher's Daughter