Heat oven to 200C/fan 180C/gas 6. Rinse the rhubarb and shake off the excess water. Trim the ends and cut the rhubarb into little finger-sized pieces. Put the rhubarb in a shallow dish or baking sheet with sides, tip the sugar over, toss together, then shuffle the rhubarb so it’s in a single layer.
Cover with foil and roast for 15 mins. Remove the foil. The sugar should have dissolved, so give everything a little shake and roast for another 5 mins or until tender and the juices are syrupy. Test with a sharp knife; the rhubarb should feel tender, not mushy, and still have kept its shape.