Shiratamako (白玉粉) is a sweet, glutinous rice flour that is made from mochigome (もち米/糯米, glutinous short grain Japanese rice). The name means “white jade powder”. It’s specially processed: according to Wagashi.net, “[Shiratamako’s] properties are significantly changed: mochi rice is washed, soaked in water and ground very finely in water (in a kind of special mill).The milk white liquid is then pressed, dried and crushed. The flour isn’t a fine powder but coarse granules.”