1.Preheat the oven to hot (220°C/200°C fan-forced).
2.Tie the beef with string at 2cm intervals. Brush the roast with 1 tablespoon of the oil; sprinkle with the salt flakes and cracked pepper. Toss the beetroot in the remaining oil; add to the roasting dish.
3.Roast beef and beetroot in a hot oven for about 20 minutes. Reduce the heat to moderate (180°C/160°C fan-forced). Roast, uncovered, for about 1 hour or until the beef is cooked as desired and beetroot are tender. Remove the beef from the oven; cover, stand for 20 minutes. Continue roasting beetroot for a further 15 minutes or until tender.
4.Meanwhile, boil, steam or microwave potatoes until tender; drain.
5.Mash the potatoes; push through a sieve or mount into a large bowl. Stir in butter then gradually beat in the hot milk and cream. Season to taste with salt and pepper.
6.Serve beef with roasted beetroot, potato puree, horseradish and fresh watercress, if desired.
Not suitable to freeze. Not suitable to microwave.Note