Step 1

Melt 25g (1oz) butter in a medium pan over a low heat. Cook the leeks and carrots for 15min until softened but not coloured. Stir in the flour and cook for 1min. Gradually add the stock, stirring constantly, until the sauce is smooth. Simmer for 10min. Stir in the mustard and double cream and check the seasoning. Add the cooked chicken and chopped parsley and tip into a 1.7 litre (3 pint) ovenproof dish. Preheat the oven to 200ºC (180ºC fan) mark

Step 2

Melt the remaining 50g (2oz) butter in a small pan. Unroll the filo pastry and cover with a clean, damp tea-towel. Put a single sheet on a board and brush with a little of the butter. Roughly scrunch up the pastry and put on top of the chicken mixture. Continue with the remaining filo until the top of the pie is covered.