This recipe can also be used with our delicious chateaubriand. To cook beef fillet to absolute perfection, use a meat thermometer. For rare beef the reading should be 55 C/130 F out of the oven, rising to 60 C/140 F after resting. For medium, 65 C/150 F out of oven to 70 C/160 F after resting, and for well done, 75 C/170 F out of the oven, to 80 C/180 F after resting. For a larger Beef En Croute, use a 750g (1lb 12oz) piece Simon Howie Beef Fillet. You will need 500g (1lb 2oz) pastry and use 150g (5oz) each of mushrooms and pate. Follow the method below, rolling out the pastry to a rectangle large enough to enclose the beef. This size beef parcel will take about 40 minutes to cook to medium/rare.