Preheat oven to 200ºC (180º fan-forced). Brush beef with half the oil, season and sprinkle half the thyme over beef.
Place onions in base of roasting dish and place beef on a rack in the dish. Add ½ a cup water to base of dish. Roast for 45 minutes for rare, 55 minutes for medium and 65 minutes for well done. For ease and accuracy use a meat thermometer.
Place fennel and sweet potato in a large baking tray, drizzle with remaining oil and season. Cook with beef for 30 to 35 minutes or until tender and golden.
Place beef on a plate, cover loosely with foil and rest for 20 minutes. Thinly slice.
To make the gravy place roasting dish with pan juices and onion on stove over medium-high heat. Add stock, bring to the boil and simmer until mixture reduces and thickens slightly. Pour in any extra juices from rested beef roast. Whisk in butter and remaining thyme.
Serve beef roast with gravy, roast fennel, sweet potato and broccolini.
Beef blade would also work well for this recipe.
Swap thyme leaves for finely chopped rosemary.
You could serve the roast with mash and peas.
Judging your roast’s degree of doneness using a meat thermometer. The internal temperature of the meat will be: Rare – 55-60ºC, Medium – 65-70ºC, Well-done – 75ºC.
You can also use tongs to test the roast’s doneness. Gently prod or squeeze the roast – rare is very soft, medium rare is soft, medium is springy but soft, medium well is firm and well done is very firm. Resting the roast before carving gives the juices in the meat a chance to redistribute, giving a juicier and more tender result.