2) Preheat the oven to 165C/Gas 3. Roast the beef for about 1 1/2 hours for rare or until an instant-read thermometer registers 62C when inserted into the centre. Cook for an additional 10 minutes for medium-rare or 20 minutes for medium doneness. Remove the roast from the oven and allow to rest for 10 minutes before slicing to allow the juices to settle. While the roast rests, make the pesto.
For the pesto:
In a food processor, combine the coriander, pine nuts, garlic, horseradish and salt. Puree until well combined. With the motor running, drizzle in 65ml of oil. Process until smooth. Add additional oil, if needed, until a drizzling consistency is reached.
1) Using a sharp knife, thinly slice the roast beef. Put a few slices of roast beef on the bottom of each sandwich roll. Drizzle the coriander pesto directly on the beef.
Cook's Note: For picnics, take the pesto along in a plastic container or squeeze bottle and add it just before eating.