I had this dish at a really nice English restaurant and wanted to figure out how to make it myself. A friend lent me a cookbook called "Pie" by Angela Boggiano and it is amazing so I tried out her recipe because it looked lovely.
500 g/1 lb ready-made puff pastry
1 egg, beaten to glaze
25 g/1 oz butter
1 onion, finely chopped
150g/5 oz chestnut mushrooms, finely chopped
2 cloves garlic, finely chopped
3 tbsp chopped flat leaf parsley
100 g/3 1/2 oz smooth liver pate
750g / 1 1/2 lb beef fillet
salt and ground black pepper
Melt butter in large frying pan and cook onion for about 5 minutes until beginning to soften. Add the mushrooms and cook for an further 5 minutes until soft and creamy. Stir in the garlic and parsley and season with a little salt and plenty of black pepper. Set aside to cool.
Beat the pate into the mushroom mixture and set aside.
Preheat the oven to 400 F/200 C.
Roll out the puff pastry on a lightly flowered surface to a sheet large enough to enclose the beef, reserving the offcuts for decoration.
Brush the edges of the pastry with beaten egg and fold the pastry over the meat to enclose it in the neat parcel, sealing the edges well. Place the meat parcel onto a baking sheet, seam side down.
Cut decorative leaves from the reserved pastry. Brush the parcel with beaten egg, decorate with leaves and chill for about 10 minutes.
Bake for 40-45 minutes until the pastry is golden and puffed up. Check doneness of the meat with a meat thermometer. Transfer to a serving board and let stand for 10 minutes. Serve cut into thick slices.