The Nihonbashi Takashimaya branch of Umezono, the Japanese sweets shop that opened in 1854 in a corner of Baion-in, a sub-temple beside Senso-ji, and took its name from the plum garden there. The awa-zenzai it became famous for isn't the red bean soup the name suggests. It's a warm mound of pounded millet under smooth koshian. They also do anmitsu and warabi mochi. Hot warabi mochi is my absolute favourite Japanese dessert.