Spring is my favorite time of year for tempura as sansai, mountain vegetables, are featured at good restaurants serving tempura. At the top of this box is udo (spikenard), which reminds me of a tender and somewhat bitter white asparagus. The other vegetable is renkon (lotus root).  Tenmatsu at Nihonbashi bridge, just between Nihonbashi and Mitsukoshi-Mae stations on the…