1. Preheat your oven to 200C.
2. Allow your joint to reach room temperature before cooking.
3. Season your sirloin joint with salt and pepper, ensuring a generous covering of fat gets a good application of seasoning, massaging into the fat if needed.
4. Roast your joint fat side up in a large heavy-bottomed tray and roast for 20 minutes, before turning the heat down to 170°C and roasting for a further 30 minutes per kg.
5. If you have a meat thermometer the perfect core temperature is 54C for rare and 60C for medium-rare.
6. Remove your sirloin from your oven and place on to a carving board, covering well with two sheets of foil. Rest for a minimum of 20 minutes, or, what we like to do, is rest whilst we make the ultimate roasties using the fat from the sirloin roasting tin.
7. Carve roughly 1cm thick slices and serve.