Preheat the oven to 180°C/gas mark 4
To make the potato gratin, peel and thinly slice the potatoes, using a mandoline if you have one
Add the cream, garlic and thyme to a pan and bring to the boil. Reduce the cream by half, add the sliced potato and gently stir so all of the potato gets a good coating of cream. Season with salt, pepper and half of the Parmesan
Place a layer the potato over the bottom of an ovenproof dish. Use a microplane to grate some black truffle over the potato, then place another layer of potato on top. Grate over some more truffle
Repeat this process until all the potato has been used. Sprinkle the remaining grated Parmesan over the top, and save a small amount of the truffle for garnish
Cook the gratin in the oven for 45 minutes to 1 hour until golden brown and tender – use a sharp knife to test the gratin, it should slide in easily. If the gratin is colouring too quickly, place a piece of foil over the top and continue to cook. When ready, remove from the oven and set aside
To prepare the côte de boeuf, place a heavy-based ovenproof pan over a high heat. Tie the steak with string to keep the shape while cooking, season the beef on both sides and add a little olive oil to the pan. Place the meat in the pan, cooking to caramelise on both sides. Add the butter, garlic and thyme and baste the beef in the butter
Place the beef in the oven with the gratin for 15–20 minutes for a medium-rare finish. Once cooked, remove from the oven and rest the in a warm place for 5 minutes
To serve, carve each côte de boeuf into equal portions and arrange on a plate. Take a spoonful of potato gratin, place next to the meat and shave the remaining truffle over the top. Serve immediately.
In partnership with Great British Chefs.