If johakuto or powdered sugar isn’t available, grind granulated sugar with a blender or food processor. If you don’t have the equipment, you can also use regular granulated sugar but mix until the mixture doesn’t have a grainy texture and it is combined thoroughly. We used johakuto sugar in this recipe. Johakuto is the most commonly used sugar in Japan and has a slightly moist texture.
When making the cookie dough, remove the butter remaining on the balloon whisk thoroughly, and add it to the bowl. This process is important to keep the measurement accurate.
Be sure to bring the egg and butter to room temperature (approx. 20°C/68°F). When you push the butter with your finger, it should be soft enough to form a dent.
The fermentation time depends on its temperature so be careful not to over-rise the dough. You can also let the dough rise in a styrofoam box filled with warm water. In that case, cover the bowl with a plastic bag and make sure the steam won’t wet the dough.