Heat the olive oil and butter in a non-stick frying pan. When hot, add the beef and seal on sides. Remove from the pan, season with salt and pepper and allow to cool completely.
For the duxelle:
In the same pan, add the butter and when hot and foaming add the shallots and cook until softened and a little golden. Add the mushrooms and cook until all the liquid evaporates.
Add the cream, salt and pepper and continue to gently heat until it has reduced to a thick puree. Set aside to cool completely.
Pre-heat the oven to 230°C/450°F/Gas Mark 8.
Roll out the pastry to a rectangle 0.25cm thick. Lay the pancakes out on top, slightly overlapping.
Make a cut about ¾ of the way through the beef into the centre of the beef fillet and fill with the cooled duxelle mix.
Place the beef onto the pancakes, brush the pastry edges with a little water and roll the pastry up to enclose the beef. Place on a baking tray seam side down. Decorate the top and brush all over with the beaten egg.
Place it in the oven for 10 minutes, then reduce the heat to 190°C/375°F/Gas Mark 5 and continue to cook for another 20-30 minutes, until the pastry is golden.
Remove from the oven to a carving board. Allow to rest for 5 minutes before cutting it into thick slices. Serve with steamed asparagus and gravy.
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