Preheat oven to 230 degrees C. Place beef in a baking dish and spread with 2 tablespoons softened butter. Bake for 10 to 15 minutes, or until browned. Remove from dish and allow to cool completely. Reserve juices.
Melt 2 tablespoons butter in a frying pan over medium heat. Fry onion and mushrooms for 5 minutes. Remove from heat and let cool.
Mix together pate and remaining softened butter and season with salt and pepper.
Spread pate over beef. Top with onion and mushroom mixture.
Roll out the puff pastry dough and place beef in the centre. Fold up and seal all the edges making sure the seams are not too thick.
Place beef in a 23cm x30-35cm baking dish or on a shallow oven tray, cut a few slits in the top of the dough and brush with egg yolk.
Bake in preheated oven for 10 minutes, then reduce heat to 200 degrees C for 10 to 15 more minutes or until pastry is a rich, golden brown. Set aside, and keep warm.
Place all reserved juices in a small saucepan over high heat. Stir in beef stock and red wine then boil for 10 to 15 minutes, or until slightly reduced. Strain and serve with beef.
Made this for my hubby's birthday dinner and he absolutely Loved it. Surprisingly simple to put together, but wow - what a sensory impact! The golden crust glistens, and crunches lightly as you slice into it, revealing the layers of colour inside. The warm, rich smell of beef, pastry and mushroom tantalises your tastebuds, which are happily rewarded for their patience as the intricate blending of flavours melt in your mouth. Superb! - 19 Jun 2010