First, make the pastry. Mix the flour and mustard powder together in a bowl. Coarsely grate in the frozen butter, stirring occasionally to coat the butter in the flour. Pour in 90-100ml cold water and mix with a cutlery knife to make a soft dough. Wrap and chill for at least 30 mins.

Heat a deep medium frying pan over a low heat and cook the bacon for 5-10 mins until it has released its fat and turned golden. Add the butter, leeks and thyme leaves. Cover and cook for 15-20 mins until the leeks are soft. Stir in the flour and cook for 2-3 mins more, then gradually pour in the stock. Stir and simmer until thickened. Scrape into a bowl and leave to cool.

Heat the oven to 200C/180C fan/gas 6. Mix the cream, mustard and turkey into the cooled leek mixture, then pour this into a 23cm pie dish.

Roll the pastry out on a well-floured surface into a 35cm circle. Brush the rim of the pie dish with a little of the beaten egg, then lift the pastry over the filling and press along the rim to seal. Trim and crimp the edges, then cut three air holes into the top of the pie. Bake for 45 mins until the pasty is golden and the filling piping hot.