Wash and dry the rhubarb. Trim the top and bottom off each stalk and discard. If any stalks are wider than 1 inch (2.5 cm), cut them in half lengthwise. Cut the stalks into ½-inch (1.2-cm) slices.
Place a stainless steel bowl in the oven until it is hot. Stir the cornstarch and sugar together in the bowl, add the rhubarb pieces, and toss to coat them thoroughly