Heat oil and butter in a pan and seal the seasoned beef on all sides.
Remove the beef from the pan and let it cool completely.
Sauté shallots in butter until soft and golden.
Add mushrooms and cook until all liquid evaporates.
Stir in cream and reduce to a thick purée, then cool completely.
Preheat the oven to 230°C.
Roll out the pastry and overlap two pancakes on top.
Spread a strip of chicken liver pate across the pancakes.
Cut three-quarters into the beef and fill with the mushroom mixture.
Place beef on pancakes, cover with remaining pancakes, and wrap in pastry.
Seal pastry edges with water and place seam-side down on a tray.
Brush the pastry with beaten egg and bake at 230°C for 10 minutes.
Reduce heat to 190°C and bake for another 20 minutes until golden.
Rest the meat for 5 minutes before carving into thick slices.