• Heat oven to 200C/fan 180C/gas 6.
  • Chop the parsnips and potatoes into chunks, then boil for 15 mins until tender.
  • Drain, reserving the water, then mash with a little seasoning.
  • Cut chicken into small chunks, then toss in the cornflour.
  • Heat the oil in a large pan, add the leeks, and then fry for 3 mins until starting to soften.
  • Add the chicken and 200ml water from the potatoes, then bring to the boil, stirring.
  • Reduce the heat, then gently simmer for 10 mins, until the chicken is just tender.
  • Remove from the heat, then stir in the lemon zest, parsley, crème fraîche and mustard.
  • Divide the chicken filling between four 300ml pie dishes.
  • Spoon over the mash and spread roughly with a fork to seal in the filling.
  • Bake for 25 mins until the topping is crisp and golden.
  • You can make one big pie if you prefer. Use a 1.2-litre pie dish and increase the cooking time in the oven by about 10 minutes.