Heat the oil in a large frying pan or saucepan over a medium heat and fry the chicken until browned all over (it doesn’t need to be cooked through at this point), about 6-8 mins. Remove to a plate, leaving the oil in the pan.

Tip the butter into the pan and fry the leeks for 8-10 mins on a medium-low heat until softened but not golden. Stir in the garlic and cook for 1 min more. Pour in the white wine and cook for a few minutes so the alcohol evaporates and the liquid reduces a little.

Sprinkle over the flour and stir until a thick paste has formed and no dry flour remains. Gradually pour in the stock, stirring well between each addition until combined, about 5 mins. Pour in the milk, then bring to a simmer and cook for 1 min, stirring all the time to prevent lumps forming. Stir in the bay leaves, thyme, browned chicken and ham. Season with lots of freshly ground black pepper and a pinch of salt (the stock and ham will add salt, so season to taste). Pour into a large pie dish (ours was 30 x 20cm). Will keep for two days in the fridge, or in the freezer for three months. Leave to cool completely first, then defrost thoroughly in a fridge overnight before continuing with step 4.

Heat the oven to 200C/180C fan/gas 6. Lightly dust the worktop with flour, then roll out the puff pastry to 1/2cm thick. Cut a disc of pastry big enough to cover the pie dish with a little overhang. Lightly brush the rim of the pie dish with some of the egg, then lay the pastry over the filling and the rim of the dish. Crimp the edges and use any pastry offcuts to decorate the pie, if you like, using the egg to help them stick. Glaze the whole pastry top with more egg, then bake for 45 mins-1 hr until golden and the filling is piping hot. The pie can be chilled before glazing for up to two days, or freeze, covered, for up to three months (you will need to freeze in a freezable ovenproof dish). Can be cooked from frozen, for 1 hr- 1 hr 30 mins until piping hot all the way through.