Heat the oil and butter in a flameproof casserole over a medium heat and fry the chicken and bacon lardons for 10-15 mins, or until evenly browned. Add the onion, carrots and mushrooms, and fry for 5 mins more. Stir in the plain flour and cook for 2 mins, then add the thyme and bay. Slowly stir in the wine and bring to a simmer, then add the stock, a little at a time, stirring between each addition. Season and cover with a tight-fitting lid. Reduce the heat to low. Cook for 30 mins, then remove the lid and cook for 15 mins more. Spoon a little of the sauce into a small bowl and mix with the cornflour, then stir this back into the coq au vin. Remove the thyme and bay. Leave to cool for 1 hr.

To make the pastry, tip the flour, salt and butter into a food processor and pulse to fine crumbs. Add half the beaten egg and 2 tbsp ice-cold water and pulse again until the dough just comes together. Add an extra 1 tbsp water if the pastry feels dry. Tip onto a lightly floured work surface and knead briefly until you have a uniform dough, then wrap and chill for at least 1 hr.

Heat the oven to 200C/180C fan/gas 6. Cut off a quarter of the pastry and roll it into a long strip on a lightly floured surface. Attach the strip of dough around the lip of a 26cm pie dish using a little of the remaining beaten egg, and use any offcuts to make decorations, if you like (we cut out a crescent and scored it to make a chicken decoration). Roll the remaining pastry out into a 30cm circle, about 5mm thick. Spoon the filling into the dish and use the rolling pin to lift the pastry circle over the dish. Crimp the edges in a decorative pattern to seal, or do this with a fork. At this stage, the pie can be wrapped and frozen for up to three months. Defrost in the fridge overnight, then continue as below. Brush with most of the remaining beaten egg and attach any decorations. Chill for 30 mins, then brush with the rest of the egg. Bake in the centre of the oven for 35-40 mins until the pastry is golden and the filling is piping hot. Leave to rest for 10 mins.

Meanwhile, make the mash. Put the potatoes in a large saucepan with a large pinch of salt, cover with cold water and bring to the boil, then reduce to a simmer and cover. Cook for 15-20 mins until the tip of a knife can be easily inserted. Drain and leave to steam-dry for 5 mins, then pass through a potato ricer or sieve, or mash with a potato masher. Fold in the butter, warm milk and chives. Season. Serve the pie with the mash.