An essential ingredient in okonomiyaki is some grated nagaimo in the raw batter. Often found in Asian markets packaged in shrinkwrapped styrofoam or packed in sawdust, nagaimo is a type of yam that is very long and tubular. It's cut in five to six-inch sections before being packaged. It's one of the few members of the yam family that can be eaten raw.
The outside skin is light brown in color and has hairy roots protruding from tiny knobs on the surface. The skin is peeled off, revealing a white flesh that is crunchy and watery like a jicama, but has a very slimy texture. This can make it hard to grip the yam when grating, so take care to not slip and cut your fingers. Some people find that the mucus gives their skin a little bit of an itchy feeling. I haven't noticed this personally. There are some Asian cultures that consider nagaimo to be an aphrodisiac.
Apart from being used in okonomiyaki, nagaimo root is also grated and added to noodles, soups, and maki rolls.
(Image: Kathryn Hill)