Heat the butter and oil in a small frying pan, add the onion, cover and cook over a low heat, until softened but not browned. Transfer to a 1.1 litre (2 pint) pie dish using a slotted spoon.

Add the chicken and cook until evenly browned. Arrange on top of the onion in a single layer. Stir the parsley, spring onions, seasonings and milk into the pan and bring gently to the boil. Simmer for 2 - 3 minutes, then pour over the chicken.

Cover with foil and bake at 180°C (350°F) mark 4 for 30 minutes, until the chicken is tender. Remove from the oven and leave to cool.

Meanwhile, roll out the pastry on a lightly floured surface until about 2.5 cm (1 inch) larger all round than pie dish. Leave pastry to relax while filling is cooling.

Cut off a strip from all round the edge of the pastry. Place the strip on the rim of the pie dish, moisten with a little water, then place the pastry lid on top. Crimp the edges, make a small hole in the top.

Beat the soured cream and the eggs together, then brush the top of the pie with a little of the mixture. Bake at 220°C (425°F) mark 7 for 15 - 20 minutes, until a light golden brown. Reduce the temperature to 180°C (350°F) mark 4.

Pour the soured cream and egg mixture into the pie through the hole. Shake the dish to distribute the cream mixture and return the pie to the oven for 15 minutes. Remove from the oven and leave to stand in a warm place for 5 - 10 minutes before serving or leave to cool completely and serve cold.