Heat your oven to 220°C/Fan 200°C/Gas 7.
Unwrap your beef and pat it dry. Let it get to room temperature. If you have a pestle and mortar, crush the chopped rosemary with a pinch of salt and pepper. If not, mix in a bowl. Rub it all over the beef.
Arrange your sliced onions in a roasting tin. Make a little bed of rosemary in the centre. Place your beef on top. If the joint is tall and thin, rest it with a cut-side down and cover the top cut-side with a square of foil to keep it moist. If it’s rounder or squarish with a good layer of fat on top, rest it fat-side facing up and cover each cut side of the meat with a little square of foil. Pour in the mug of water.
Slide onto the middle shelf of the 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, covered, in a warm place for at least 30 mins (longer if you can).
Make your gravy while the beef rests. Spoon your onions into a pan. Strain in the roasting tin juices, discarding the rosemary you cooked the beef on. Sizzle over a medium high heat to reduce the liquid and to soften the onions further. Once the onions are meltingly sweet, swirl in 1 tbsp balsamic vinegar. Cook for 2 mins. Taste and season.
Add red wine or beef stock if you want a richer gravy. Let it reduce down. For a thicker gravy, place 2 tbsp flour in a mug. Spoon in 4-6 tbsp of the gravy. Whisk till you have a smooth paste. Gradually add the paste to the onion gravy and cook till it thickens. Repeat the process till you have the perfect consistency. Season to taste.
Thinly slice the beef. Drizzle the onion gravy over the top.
Need a hand?
For tips on checking your joint’s ‘doneness’ before carving it, see our How to Cook the Perfect Steak video on our website abelandcole.co.uk/recipes/the-perfect-steak
Perfect in our Thai Beef Salad recipe. Find it at abelandcole.co.uk/recipes