Preheat oven to 180ÂșC Gas Mark 4
Peel and chop the onions and garlic.
Add the butter and olive oil to a pan on a moderate heat.
Melt the butter and then fry the onions and garlic until they start to colour.
Chop the chicken into pieces and add to the pan.
Cook for five minutes until the chicken is sealed.
Chop the leeks and add to the pan with the flour.
Stir until combined
Add the wine and the chicken stock slowly into the pan stirring until the sauce thickens.
Once the sauce is thick add the cream and mustard.
Season with salt and pepper.
Remove the pan from the heat and stir in the prunes, herbs and cheese.
Add the filing to a pie dish.
Mix the egg yolk and cream together and brush around the pie dish.
Cover with pastry and trim the sides with a knife.
Brush the rest of the egg mix onto the pie.
Make a couple of holes in the pastry to let out the steam.
Cook in the oven for 25 minutes.