Pre-heat oven to 180ºC.

Sift flour into a bowl, then work the butter through the flour until it starts to resemble breadcrumbs. Add water one tablespoon at a time and mix until it comes together into a rough dough then knead on a well-floured surface. Divide the dough into two, then roll a the base and place into a well-buttered pie dish. Roll the top and leave aside while you make the filling.

Heat a little rapeseed oil on a frying pan and fry until the mushrooms are browned. Leave aside in a bowl. Then add the onion to the pan and cook until it starts to turn translucent. Add in the garlic, carrots and leeks and stir well. Then cover the pan with a lid and sweat the vegetables for about 10 minutes.

Stir in the flour and mix well, then cook over medium heat for about 1 minute. Then slowly pour in the stock stirring well as you pour to avoid lumps forming in the sauce.

Bring the heat up on the sauce until it starts to bubble then remove from the heat.

Stir in the chicken, creme fraiche, thyme leaves and mustard.

 Fill the pie with the filling, then add the top pastry. Brush the opening with a little egg wash to make them stick together, then cut 2 air holes in the centre.

Bake for 35 minutes, or until the pastry is golden brown.

Serve warm