Heat your oven to 220°C/Fan 200°C/Gas 7. Unwrap your beef. Pat dry. Put in a roasting tin and leave to get up to room temperature.
Dust the garam masala over the beef. Rub it all over to coat. Halve your chilli lengthwise. Rub the cut side of each chilli half all over the beef for a little heat. Slip the chilli under your beef if you want a spicy kick to your gravy.
Cut two squares of foil and cover the cut sides of the beef to keep it moist, allowing just the fat to be directly exposed to the heat. Dust the exposed fat with a good pinch of sea salt.
Slide onto the middle shelf of your oven. Turn the heat down to 180°C/Fan 160°C/Gas 4. Roast for 45 mins for rare, 1 hr for medium and 1 hr 15 mins for well done.
Remove the beef from the tin and rest on a plate in a warm place, covered in foil, for at least 30 mins (longer if you can).
While the meat rests, roll your pomegranate firmly on the table with the palm of your hand to loosen the seeds.
Set a sieve over a bowl. Cut the pomegranate in half and hold over the sieve. Whack the back of each half with a wooden spoon, letting the bowl catch the juices and the sieve catch the seeds. Turn each pomegranate half inside out to reveal any remaining seeds and pick them out.
Drizzle the pomegranate juice into the tin with your meat juices. Set over a medium heat on the hob to warm through.
Thinly slice the beef. Cut out any stringy bits. Arrange on a platter. Drizzle the warmed juices over the sliced beef. Sprinkle with a little salt, a pinch of any remaining garam masala and the pomegranate seeds.