To make the pastry cases, roll out the pastry to 5mm/Â_" thick and cut into 10cm/4" squares. Place on a wetted oven tray. To make the lid, cut an inner square with a sharp knife halfway through the pastry, leaving a 1cm/Â_" border. Mark a pattern on the surface of the inside square and brush the tops with egg glaze. Chill 30 minutes.
Bake in a pre heated oven at 220Â°C/425Â°F/Gas mark 7 for 15 minutes until the cases are well risen and golden. Reduce the temperature to 190Â°C/375Â°F/Gas 5 and cook a further 10 minutes. Carefully cut round the lids and remove, return to the tray, upside down, to crisp the underside. Scoop out the soft dough from the inside of the cases then return to the oven for 5 minutes. Keep warm while making the filling.
While the pastry is cooking put the stock and champagne or wine into a pan and boil for 5 minutes to reduce the volume to 300ml/Â_ pint. Cut the turkey into short strips, 5mm/Â_" wide.
Heat the oil and butter in a frying pan, cook the turkey for 4 - 5 minutes, remove and set aside. Add the shallot to the pan, cook 2 minutes, then add the mushrooms and cook 2 - 3 minutes until tender. Pour in the reduced stock and cream, return the turkey and simmer 2 minutes. Stir in tarragon and seasonings. Blend the cornflour with a little water, add to the pan, stirring, and heat to thicken.
Divide the turkey filling between the pastry cases and serve.