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1
Score an X on the flat side of each chestnut shell. Boil the chestnuts for 3 minutes. Remove one at a time, keeping the rest warm in the water, and peel away both the outer shell and the inner brown skin (shibukawa) completely. Any shibukawa left will introduce bitterness to the rice.
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2
Drain the soaked mochigome thoroughly. Combine dashi, soy sauce, mirin, sake, and salt in a bowl and stir to dissolve the salt. Add the drained rice and stir briefly to coat, then add the peeled raw chestnuts and fold them through gently so they distribute evenly among the grains.
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3
Bring the steamer to a rolling boil. Line the steamer basket with a dampened cotton cloth or muslin. Spread the rice and chestnut mixture evenly in the lined basket, leaving a small well in the centre for steam circulation. Pour any remaining seasoned liquid evenly over the surface. Set over the boiling water and steam, covered, for approximately 45 minutes. This is where the dish lives or dies: insufficient soaking or steaming time leaves hard, chalky centres in both rice and chestnut, while the correct 45 minutes transforms the rice to its characteristic sticky, chewy texture and the chestnuts to tender gold.
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4
At the halfway point — approximately 20–25 minutes — lift the lid and stir the rice gently with a dampened rice paddle, turning the outer grains toward the centre and redistributing the chestnuts. Replace the lid and continue steaming for the remaining time. Even heat distribution is confirmed when no dense, dry pockets remain at the surface.
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5
The rice is done when each grain is uniformly translucent, cohesive, and pulls with a distinct chew; the chestnuts yield cleanly under light pressure without resistance or crumbling. Turn into a serving vessel, scatter black sesame seeds (kurogoma) over the surface for visual contrast and depth, and serve promptly.