Chicken and mushroom puff pie

Ingredients

• Skinless boneless chicken thighs – 8 nos.
• Vegetable oil – 1 tablespoon.
• Smoked streaky bacon – 8 rashers. (They should be cut into large pieces).
• Plain flour – 2 tablespoons.
• Halved and sliced onion – I no.
• Thyme sprigs – handful.
• Baby button mushrooms – 250 gram pack.
• Milk – 200 ml.
• Beaten egg- 1 no.
• Chicken stock – 400 ml.
• Fresh puff pastry – 500 gram pack. (Or frozen and defrosted).