Cylinder casserole. Roasting vegetables refers to a cooking method that uses steam to ripen food in a closed container. Roasted vegetables come from Hakka dishes. It is a cooking method that uses soup, steam, salt or hot air as heat transfer medium to heat pickled materials or semi-finished products until cooked. Use a cylindrical casserole. The traditional casserole is a ceramic product made of raw materials that are not easy to transfer heat, such as seasonable, feldspar and clay, and is fired at high temperature.