Instructions

1. Preheat the oven to 200°C.
2. Put the potatoes in a pan of cold water, bring to the boil and cook for 12- 15 minutes, until just tender.
3. Meanwhile, mix the mustard, oregano, oil, lemon juice, one clove of minced garlic and some ground peppercorn.
4. Using a silicon brush, coat the beef with this paste. Put it in a roasting tray then roast in the middle of the oven for 20 minutes.
5. By now the potatoes should be tender, so drain them and cut into bite sized pieces.
6. Cut the onion into wedges.
7. After 20 minutes of roasting take the beef out of the oven, and reduce the oven temperature to 180C.
8. Scatter the onion and potato pieces around the beef and brush them with the paste. Add the thyme leaves.
9. Roast for another 20/25/30 minutes per 500g during which turn over the potatoes and the beef and brush them with the remaining paste at lest twice.
10. For the last 5 minutes scatter the remaining garlic and the lemon zest over the potatoes.
11. Rest the meat (covered with foil) for 15 minutes before carving. If the potatoes are not crispy enough, put them back in the oven for a few more minutes (lemon zest and garlic should be added during the last 5 minutes of the roasting)