When the Cauliflower is roasted and golden all over ... To make the tahini sauce, peel and roughly chop the garlic. Add that and the lemon juice to a blender and blitz for a minute.
Cook garlic, stirring occasionally ... 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.