For the roasted rhubarb, preheat the oven to 200C/400F/Gas 6. Cut the rhubarb into 15cm/6in or so lengths (about the length of a wooden spoon-handle) and place in a roasting tin with half a tea-cup of water and the light brown sugar. Roast until just soft enough to take the point of a knife, about 10-15 minutes. Allow to cool, then drain, reserving the cooking juices.
Use in sweet or savoury dishes, such as a rhubarb tart or with fried mackerel fillets.