Pat beef dry. Tie with twine if loose. Rub all over with salt. Refrigerate uncovered overnight, or at least 1 hour.
4-4.5 lbs topside roast, 2 teaspoons salt
Take out of fridge 1 hour before roasting. Heat oven to 190°C (170°C fan, 375°F).
Cut garlic into halves or thirds. Make slits in the beef and push garlic in.
4 garlic cloves
Mix zest, rosemary, pepper, and oil. Rub over the beef.
Zest from 1.5-2 medium oranges, 1 tablespoon olive oil, 1 sprig of fresh rosemary, 2 teaspoons ground black pepper
Set beef on middle rack with a roasting tin below. Roast 30 minutes.
Reduce oven to 110°C (90°C fan, 225°F). Roast until the thickest part reads 52-54°C (125-130°F) for medium-rare, about 1 hr 45 min for 1.87kg. Start checking 30 minutes early.
Rest 30 minutes, loosely covered with foil.
Remove twine. Slice thinly across the grain.