Tempura is one of Japan's great contributions to the world of frying — seafood and vegetables dipped in a thin, cold batter and cooked briefly in hot oil so the result is almost weightless. The technique was introduced by Portuguese missionaries in the 16th century and then refined by Japanese cooks over centuries into something quite different from anything in Europe.
Good tempura is about restraint: the batter should be barely mixed (lumpy is fine), the oil must be at the right temperature, and the pieces should be eaten immediately. In a traditional tempura restaurant, the chef fries each piece to order and serves it directly to your plate. Classic items include prawns, white fish, sweet potato, shiso leaf, and lotus root. Eat with a light dipping broth (tsuyu) and grated daikon.
You'll find tempura everywhere in Japan — as a donburi (tendon) over rice, as part of a bento, or as a topping in udon and soba. For the real thing, a dedicated tempura restaurant is worth the splurge.