Street vendors in Japan can be seen using long wooden mallets to make mochi dough, sometimes taking turns smashing the rice like two blacksmiths across an anvil, doubling their power and speed. For sweet mochi, specialty rice flours can provide a shortcut and require way less muscle.

Behind the counter at her shop, with her hair tucked behind a brightly colored bandanna, Ms. Kato measured out sugar, water and shiratamako flour, which she likes for the smooth, elastic quality it lends the finished dough. Mochiko flour, more commonly available (and sometimes called sweet rice flour or glutinous rice flour), will also get the job done.

After Ms. Kato whisked the gritty-looking shiratamako with water, the tiny pellets dissolved completely. She poured the slurry through a strainer just in case, then added the sugar.

This basic mixture could be steamed in a double boiler, or even blasted for a few minutes in the microwave. But Ms. Kato stirred the ghostly white liquid in a pan on the stove until it thickened, first into a sticky, lumpy paste, and then into a heavier, tighter mass. It was nearly there.