Chicken: If you are using a fresh chicken, season well and drizzle with olive oil, chop the onion, carrot and celery into 3cm (1 inch) pieces and place in the bottom of a roasting pan.
Put the chicken on top of the vegetables and add a little water to the bottom of the pan.
Roast at 180 Celsius (350 Fahrenheit) for 1 ½ hours until golden brown, basting every half-hour, until a thermometer (inserted) reaches 165C (329F) or juices run clear.
Let the chicken cool, then remove skin and bones and cut into 3cm (1 inch) chunks, (do the same for a rotisserie chicken).
Sauce: To make the sauce melt the butter in a saucepan, then add the flour and stir with a wooden spoon; cook for a minute before adding the chicken stock, do this in 3 stages whisking well to incorporate.
Add the milk in the same way and then the cream and the wine.
Whisk in the chicken cube and then season well with salt and pepper.
Let the sauce simmer for 3-4 minutes.
Vegetables: Place the chopped carrots in a pot of cold water with a pinch of salt, bring to a boil, cook for 5 minutes until tender, then drain.
Heat a sauté pan, when hot add the olive oil and butter, once melted add the pancetta.
Cook for a few minutes until starting to color, add the mushrooms and pearl onions, cook for 4-5 minutes until golden brown.
Combine: Add chunks of chicken to the sauce, then the rest of the ingredients, and stir well to combine.
Taste and correct the seasoning if necessary.
Pour the mixture into a pie dish approximately 23cm x12cm. (9”x 4.5”). *Or if you prefer you can use individual pie dishes (ramekins).
Pastry: Roll out the puff pastry a little on a floured surface.
Make an egg wash for the pie by adding a tablespoon of cold water to the egg yolks.
Brush the rim of the pie dish with egg wash, then cut a 1cm (.4 inches or just under 1/2 inch wide) strip of pastry and place all around the edge of the dish.
Brush eggwash onto this pastry then lay the rest of the pastry on top.
Trim the pastry from the sides, leaving a 2cm ( .78 or just under 1 inch wide) edge on the side. Using your thumb and finger, press the pastry together to form a decorative edge or use the back of a fork pressing down to form a pattern.
Brush the whole pie with eggwash and score in a criss-cross pattern with the back of a knife.
Make three slits in the top of the pie top allow the steam to escape.
Bake: Place in the center of a pre-heated 180C (350F) oven and bake until golden brown, around 30 minutes. *If you are using individual pie dishes (ramekins) cover with pastry the same way and bake for around 20 minutes.