1. Soak the porcini mushrooms in cold water for 20 minutes. Meanwhile, heat the butter and saute the onion and chopped mushrooms slowly until soft and the liquid has evaporated. Leave to cool.
2. Heat the oil until hot in a large non-stick frying pan, season the meat and brown on all sides. Lift out the beef, reserving the juices, and leave to cool.
3. Drain the porcini mushrooms and add the liquor to meat juices. Chop the mushrooms and add to the onion mix.
4. Roll out the pastry on a floured surface to a rectangle 35x25cm (14x10 inches). Trim the edges and spoon one third of the mushroom mix over the centre and sit the beef on top. Spread remaining mix over the top. Brush edges of pastry with the egg and wrap the pastry over the meat to encase completely.
5. Place the seal underneath and use pastry trimmings to make the decoration. Cover and chill until required.
6. When ready to cook, place on a greased baking sheet and brush with the egg. Bake in a pre-heated oven at 220°C (Gas Mark 7) for 30-35 minutes for rare, or 5 minutes longer for medium-rare.
7. While the beef rests for 5-10 minutes, reheat the reserved juices with the knorr gravy pot and 280ml water. Whisk until boiled and thickened. Serve the gravy with the beef cut into 6 thick slices and garnish with fresh thyme. Serve with new potatoes and a selection of vegetables.
Recipe courtesy of Kenwood's Around the World in 80 Plates