Mix the red bean paste with diced chestnuts until smooth, then divide into several equal portions.
Place ingredient A in a pot and heat over low heat, stirring constantly until thickened. Add granulated sugar and continue stirring until the moisture evaporates and the mixture becomes even more viscous. Add maltose syrup and turn off the heat. Add matcha powder mixed with a little water and stir until completely transparent and chewy.
Transfer the mixture to a flat plate covered with tapioca starch. Sprinkle another layer of tapioca starch on top and press it down to about 0.8 cm thick. Use a round mold to cut out round mochi pieces.
Place the red bean paste/chestnut filling in the center of each mochi piece and fold the mochi in half.
