A cauliflower’s outer leaves provide natural protection for the white florets (or 'curds', as they are sometimes known). Look for heads with firm, white florets without blemishes – if they do have the odd black or brown patch, simply cut these off and discard (the rest of the vegetable should be fine). The leaves are a great indicator of the vegetable's health; ideally they should be firm and vibrant green with no yellow or black spots. If the leaves and stalks (or ‘ribs’) are healthy, avoid wasting them – they can be shredded and stir-fried, simmered in stocks or roasted with the rest of the vegetable.