Preheat your oven to 200°C (180°C fan).
In a large pan, melt the butter and sauté the leeks until soft.
Add the diced chicken and cook until browned.
Pour in the white wine to deglaze for 3 - 4 minutes
Stir in the flour and cook for 2 minutes.
Gradually add the chicken stock, stirring continuously until the sauce thickens.
Add the cream and season with salt and pepper.
Transfer the mixture to a pie dish.
Cover with puff pastry, sealing the edges.
Brush the top with beaten egg.
Bake for 40 -50 minutes or until the pastry is golden brown and the filling is bubbling.
Serve with green beans and potatoes