1. For the butter, heat the oil in a heavy-based pan over a medium-low heat. Add the anchovies and cook for 3-4 minutes until they have dissolved, stirring frequently.
2. Add the onion and sugar and cook for 45 minutes until caramelised, stirring frequently. Add a splash of water if needed to stop the onions from catching on the bottom of the pan.
3. Remove from the heat and allow to cool to room temperature.
4. In a food processor, combine the cooled caramelised onions and butter. Pulse until smooth. Use parchment paper to form the butter into a log. Wrap up tightly, then place in the fridge until firm.
5. Remove the rib roast from the fridge 30 minutes before you start cooking. Preheat the oven to 180°C/160˚C fan/gas mark 4.
6. Heat the oil in an ovenproof pan over a high heat. Brown the rib roast on all sides.
7. Place a knob of the caramelised onion butter on top of the rib roast, then transfer the pan to the centre of the oven and cook for 6 minutes for rare, 8-10 minutes for medium-rare, 14 minutes for medium or 16-17 minutes for medium-well.
8. Transfer to a plate, tent loosely with foil and allow to rest for 15 minutes.
9. Carve the steak and divide between plates, then top each with a generous slice of the caramelised onion butter and serve with baked potatoes and green beans.

Note: rapeseed oil can be used as an alternative to olive oil, if you wish.

Per serving: 822kcals, 58.1g fat (25.3g saturated), 2.7g carbs (1.3g sugars), 69.1g protein, 0.6g fibre, 3.16g sodium

Recipe courtesy of Lidl – try their tasty Irish rarebit rib-eyes!