Method

1. Preheat oven to 220°C / 425°F / Gas Mark 7
2. Heat a large frying pan, melt the butter and oil, and then add the sliced onion and leeks. Cover and cook very gently
3. After 5 minutes, add the cubed potatoes and cook for a further 10 minutes until the onion, leeks and potatoes are soft
4. Stir in the flour, turn up the heat, then gradually add the stock, stirring until the mix thickens a little.
5. Take off the heat, then stir in the crème fraîche, mustard and add the cooked turkey and ham
6. Season to taste, then cool - if you have time
7. Spoon the mix into a large pie dish, add a bay leaf and the chopped parsley (this mix can be made up to a day ahead and kept chilled)
8. Trim pastry to fit the top of the dish and brush around the edges with a little water to help it stick, then press down along the sides to seal
9. Cut a few slits to let the steam escape, then brush all over the top with beaten egg. Bake for 30 minutes until risen