Heat the oven to 220C/Gas 8. Tear the chicken flesh from the bone in large chunks and discard the skin and bones.
Heat the butter in a large pan, add the leek and cook for 5 mins or so, until softened and lightly coloured.
Stir in the flour and cook for 1 min and then gradually add the milk, stirring continuously.
Add the cream and simmer until the sauce thickens, then stir in the chicken, tarragon and Comté.
Roll out the pastry to the thickness of a £1 coin and cut 4 circles big enough to cover 4 small pie dishes (or for one big pie).
Divide the mixture between the dish/es and brush the rim/s with beaten egg. Lift the pastry on to the pie(s), trimming off any excess. Press down and crimp the edges with a fork. Cut a couple of slits in the pastry to let the steam out and brush all over with the rest of
the egg.
Bake for 15-20 mins (30-40 mins if one big pie), until the pastry is crisp and golden brown.
Recipe by appetite magazine at https://www.appetitemag.co.uk/creamy-leek-chicken-and-comte-cheese-pie/