Heat the butter in a large non stick frying pan and add the mushrooms, cook stirring for 5 minutes until softened. Remove from the heat and spoon into a food processor with the tarragon, orange zest, soft cheese and breadcrumbs. Blitz to combine thoroughly then season to taste.
Preheat the oven to Gas Mark 6, 200°C, fan 180°C. Spread the mushroom mixture over the top and sides of the Quorn family roast. Roll out the pastry to a rectangle large enough to enclose the Quorn roast. Lift the Quorn roast on to one side of the rolled out pastry, brush the pastry edges with beaten egg and fold the other side of pastry over the roast to enclose it.
Press the edges down well to seal, trim any excess pastry and pinch the edges together between you thumb and forefinger. Brush the whole thing with beaten egg, lift onto a nonstick baking tray. You can decorate the top with any pastry trimmings if you wish, then bake for 55 minutes until pastry is well risen and golden.
Serve sliced with freshly cooked vegetables such as green beans, asparagus, baby carrots and crispy roasties.
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