Place the flour and 20g of butter into a saucepan and cook over
a medium heat, stirring for 1-2 minutes.
With the pan on a medium heat, gradually stir or whisk in the
stock, followed by the cream, then add the diced chicken.
Bring to the simmer, season with salt and ground white pepper
and cook gently for 12-15minutes.
In a separate pan soften the onion in the remaining butter,
then add the leek and finally the mushrooms, cooking until tender
without any colour.
Add this mix and the diced wood smoked lardons to the chicken
mix.
Remove from heat and chill, adding the tarragon when cool.
Spoon the filling into a large pie or baking dish (approx. 20 x
30cm) with a lip, this can be done the previous day or in the
morning ready to finish.
Heat oven to 190ºc fan assisted or 200ºc for ovens without a
fan.
On a floured surface, roll the pastry to the 5-6mm thick.
Cut a long strip as wide as the rim of the pie dish and, using
a little of the egg, fix to the edge of the pie dish. Brush with
egg, then lift the rest of the pastry over the pie, using the
rolling pin to help.
Gently press the edges with your fingers and trim with a sharp
knife.
Make 3 slits in the middle of the pie to allow steam to
escape.
Brush lightly with egg to glaze, then bake for 30 mins until
the pastry is golden brown.