Roast beef with carrot, horseradish, duck fat potatoes & marrows

For the roast, season the meat the day before to improve flavour, browning and texture. Plan 250g meat per person. Transfer the meat to a wire rack, set in a foil-lined rimmed roasting tray and refrigerate uncovered, at least overnight and up to 2 nights. When ready to cook: adjust the oven rack to centre position and preheat the oven to 110°C. Place the roasting tray with the wire rack and sirloin in the oven, and roast until the internal temperature registers 50°C on an instant-read thermometer, 2 – 3 hours. Remove from oven and set aside at room temperature, 10 minutes. To finish the roast under the grill: adjust the rack to 15cm from the grill element and preheat the grill to high. Heat the butter, swirling, in a small saucepan over high heat until the foam subsides and the butter turns a light, nutty brown. Add the thyme and onions and stir until the crackling stops. Pour the butter mixture over the sirloin and spread it evenly with a spoon until all surfaces are coated. Remove the onions from the top surface of the meat. Place the pan with the sirloin under the grill, turning every 30 seconds, until well browned on all sides and an internal temperature registers 50°C for rare or 58°C for medium-rare, about 2 minutes in total. Alternatively, to finish the roast on the stovetop: heat the butter, swirling, in a medium frying pan over high heat until the foam subsides and the butter turns light, nutty brown. Add the sirloin, onions and thyme, and cook, turning occasionally. Spoon the hot butter and aromatics over the roast until well browned on all sides, and an internal temperature registers 50°C for rare or 58°C for medium-rare, about 1½ minutes. Transfer the sirloin to a cutting board and allow to rest, 5 minutes.

For the horseradish cream, while the beef is roasting, pour the cream into a large bowl. Whip the cream until stiff peaks form and fold in the horseradish. Season with Tabasco and salt.

For the carrot purée, combine the carrots, carrot juice and salt in a large pot. Cover and simmer over low heat until very soft, about 20 minutes. Remove the lid and reduce the liquid until almost dry. Blitz the carrots and remaining liquid in a blender on high speed until very smooth. Pass the purée through a fine mesh sieve or chinois (a cone-shaped sieve).

For the baby marrows, heat the olive oil in a shallow pan and add the marrows. Stir-fry over high heat, a few minutes. Lower the heat and cook the marrows until just tender. Season with salt, pepper and truffle oil. Place the baby marrows in a bowl and sprinkle them with the Parmesan.

For the potatoes, preheat the oven to 220°C. Place the duck fat in a roasting tray and place the tray in the preheated oven. When the fat has melted and it is hot, carefully arrange the potatoes and herbs in the tray. Return the tray to the oven and roast the potatoes until golden, about 20 minutes. Season to taste.

Slice the roast into 2cm-thick slices and sprinkle with the sea salt and chives. Arrange the sliced meat and onions on a serving plate or platter and serve with the horseradish cream. Place some dollops of carrot purée on the plate. Serve the potatoes and baby marrows on the side and garnish with roasted vine tomatoes, if desired.