1. In a large dish mix together the salt, pepper, sugar, wine and onions.
2. Pour the mixture into a large double-lined plastic food bag. Add the beef and coat all over with the mixture. Seal, place on a large plate and refrigerate overnight.
3. Preheat the oven to Gas mark 6, 200°C, 400°F.
4. Remove the joint from the marinade mixture and pat dry. Heat the oil in a large non-stick frying pan and sear the joint all over until brown.
5. Transfer to a metal rack in a large non-stick roasting tin and open roast for 25 minutes (rare) or 35 minutes (medium). Remove from the oven and set aside to cool for 30 minutes.
6. Place a large square of aluminium foil over a chopping board and scatter with half the herbs.
7. Position the beef on top of the herbs, pressing down to coat evenly then scatter the remaining herbs on top. Wrap up tightly in the foil and refrigerate for up to 2 hours.
8. Thinly slice and serve at room temperature with bay infused potatoes.

Bay Infused Potatoes:

1. Place the potatoes, onions, garlic and bay leaves in a large pan of boiling, salted water and cook for 15-20 minutes, or until almost tender. Drain and set aside to cool. Remove and discard the garlic cloves and bay leaves. Cut the onions into wedges.
2. Heat the butter, oil and paprika in a large non-stick pan over a moderate heat. Add the potatoes and onion wedges, tossing gently. Cook for 3-4 minutes.
3. Transfer and serve with the cured beef fillet.