Preheat oven to 500°F. In a bowl, combine salt, mustard powder, garlic powder, pepper, thyme leaves and olive oil.
Pat beef dry with paper towels and rub the spice mixture all over the meat.
Place on the roasting pan and bake for 15 minutes.
Reduce heat to 325°F and continue baking for about 1 hour and 30 minutes for medium doneness, or about 30-40 minutes per kilo of meat.
Let rest for 20 minutes before carving.