- Start by making your pastry. In a food processor blitz together the flour, butter and parmesan until it resembles breadcrumbs, add sour cream and sea salt and pulse until a rough dough forms. Turn out onto a lightly floured bench and gently bring together until smooth. Shape into a ball and wrap in plastic wrap and allow to rest in the fridge for 20mins.
- Preheat oven to 220C. While the pastry is resting, make a start on the filling by heating a large non stick frypan over high heat, add oil and cook chicken in batches, until lightly coloured, remove and set aside.
- To the same fry pan add leek and butter, reduce heat and gently sweat down the leek for 3-4 mins. Add garlic, thyme, tarragon and mustard. Stir well to combine. Add chicken pieces and cook for a further 3 mins seasoning well with sea salt and pepper.
- Sprinkle over flour and stir to coat all the chicken, cook over low heat for 3-5mins then pour over cream and chicken stock. Bring to a gentle simmer stirring well to incorporate flour and create a silky sauce*. Add filling to a 25cm (1.5L) pie dish.
- Remove pastry from fridge and roll out to 5mm thickness in the shape of your pie dish. Cover filling with pastry, crimping the edges. Cut a small hole in the centre of the pastry top and brush with egg wash. Bake for 10mins at 220C and then reduce temperature to 180C and cook for a further 20-25mins. Allow to cool slightly before serving.
* If the sauce is looking thick, do not worry, this will loosen slightly when pie is baked in the oven.