Cook the potato in a large saucepan of salted water for 15-20 minutes until tender.
Meanwhile, melt butter in a saucepan set over a medium heat and sweat the leek with a little seasoning until soft. Remove from the heat once softened. Drain the potatoes when they are tender and leave to steam for a minute before mashing with the cornflour and seasoning until smooth.
Add the sweated leek and chopped tarragon and mix until smooth. Take generous tablespoons of the mixture and shape into 5cm pucks. Heat the sunflower oil in large frying pan over a medium heat until hot.
Fry the potato cakes for 2-3 minutes on both sides until crisp and lightly browned. Drain on kitchen paper before serving.
*costings based on using leftovers.
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