Kashiwa oak leaves
Large, scalloped leaves of the Japanese daimyo oak, used to wrap rice cakes. They lend a faint, slightly astringent fragrance and are not eaten.
Kashiwa leaves come from the daimyo oak (Quercus dentata), whose leaves have long been used in Japan to wrap rice cakes, above all kashiwa mochi for Children's Day in May. The leaf itself is tough and is peeled away before eating. It does, however, give the filling a delicate, green, slightly woody and astringent aroma, and it keeps the sticky dough from clinging to your fingers. Outside Japan they are almost only available dried or preserved in brine and vacuum-packed, from well-stocked Asian grocers with a Japanese range or by mail order. Brined leaves should be rinsed and briefly soaked before use, dried ones softened in hot water.
Substitute:
There is no true substitute, because the leaf's particular fragrance cannot be reproduced with anything else. If you only need a wrapper for handling, bamboo or banana leaves will do, but the dish loses its characteristic aroma. Local oak leaves gathered outdoors are not suitable, as they have not been prepared for food use.