For the beef, preheat the oven to 200C/390F/Gas 6.
Heat a frying pan until very hot. Season the beef with salt and freshly ground black pepper and brush with a little olive oil. Add the beef to the hot pan. Fry on all sides in the hot pan until nicely browned.
Transfer the beef to a roasting dish and place in the oven to cook for 1 hour 10 minutes for rare.
Remove the beef from the oven, cover with aluminium foil and rest in a warm place for 15-30 minutes.
For the Yorkshire puddings, place the flour into a bowl and season with salt and freshly ground black pepper.
Add the eggs and milk to the bowl and whisk to make a smooth batter.
Add the grated horseradish and whisk again to combine. Cover and place in the fridge to chill for at least one hour, but preferably overnight.
Preheat the oven to 220C/430F/Gas 7. Divide the dripping or lard between 2 x 12-hole muffin tins or Yorkshire tins.
Place the tins in the oven for ten minutes until smoking hot.
Carefully pour the batter into the tins, filling the tins two-thirds full.
Place the tins into the oven and cook the Yorkshire puddings for 20 minutes - do not open the door during this time.
After 20 minutes, open the door to allow any steam to escape and turn the temperature down to 190C/375F/Gas 5. Continue to cook until the Yorkshire puddings are golden-brown and crisp.
For the leek gratin, preheat the grill to high.
Heat a frying pan until hot, and add the butter, olive oil and leeks. Fry over a low heat for 1-2 minutes until just softened.
Add the white wine to the pan and simmer for a further two minutes, until the wine has reduced by half.
Add the double cream and cook for a further minute. Season with salt and freshly ground black pepper, to taste, and spoon the creamy leaks into an ovenproof dish.
Sprinkle the grated cheese over the top of the gratin and place under the grill to cook until golden-brown.
To serve, remove the fat from the juices in the beef roasting dish and set it aside to use for another dish (such as for cooking chips).
Place the roasting dish over a low heat to reheat the juices. Carve the beef into individual ribs.
To serve, arrange one rib on each serving plate. Place a spoonful of gratin and a couple of Yorkshire puddings on the side of each portion of beef, spoon the juices over and serve.