Step 1

Pour water into a large wok or saucepan to come 3" up sides. Bring to a boil and set bamboo steamer on top. Line steamer with damp cheesecloth; sprinkle with sugar (this helps prevent rice cakes from sticking).

Step 2

Whisk together 1 cup sweet rice flour (mochiko) and ⅓ cup sugar in a medium bowl. Add 1 cup room-temperature water and whisk until incorporated and mixture is lump-free. Pour mixture into steamer basket, cover, and steam, adding more water to wok or saucepan if needed, until rice cake is opaque and firm, 40–45 minutes.

Step 3

Generously sprinkle a work surface with cornstarch. Carefully invert rice cake onto surface and slowly peel away cheesecloth, using a wet spatula to help scrape off dough if needed. Let cool 5–10 minutes.

Step 4

Evenly sprinkle rice cake with ½ cup roasted soybean powder; pat to adhere. Cut rice cake into 1½" squares with a sharp knife. Working with 1 piece of rice cake, gather all the corners and pinch together to form a teardrop shape, then roll between your palms into balls; repeat with remaining rice cakes. Sprinkle with more roasted soybean powder to coat; pat to adhere. Sprinkle with remaining 2 tsp. sugar. Serve warm or at room temperature.