Brush cauliflower with half of garlicky oil. Loosely cover with foil. Roast cauliflower until just tender, 35 to 40 minutes. Uncover and continue to roast until very tender, about 10 minutes more.
Preheat the oven to 200C/180C Fan/Gas 6. Put the cauliflower in an ovenproof dish and season with a pinch of salt and pepper. Roast for 20 minutes, or until tender and starting to brown.
Garnish a bowl of chewy, nutty farro with roasted cauliflower florets, which turn sweet as they brown. The pair make a light vegetarian meal or a side for roast chicken or broiled fish.