¼ cup brown sugar
⅓ cup warabi starch, such as hon warabiko or warabi mochiko (or substitute tapioca starch, sweet potato starch, or potato starch)
2 tablespoons sugar
Soybean flour, for dusting
In a small saucepan over medium heat, combine brown sugar with ¼ cup water to make the brown sugar syrup.
Bring to a boil, stirring constantly with a wooden spatula or spoon until sugar completely dissolves.
Transfer to a bowl to cool to room temperature.
To make the warabi mochi, prepare a large bowl of ice-cold water.
In a medium saucepan, whisk together warabi starch, sugar, and 1 cup water into a uniform batter.
Place saucepan over medium-low heat, stirring continuously until the mixture thickens and becomes transparent.
Scrap the mixture into the bowl of ice water. Use your hands to squeeze and pinch off small pieces of the dough, keeping each piece submerged in the bowl of cold water until ready to serve.
Strain the warabi mochi into a shallow bowl.
Sprinkle the warabi mochi with a generous amount of nutty soybean flour and drizzle with brown sugar syrup.
Use a dessert spoon to serve warabi mochi immediately.