Boil up the mirin, chicken stock and soy sauce. Add sugar and stir until dissolved. Bring to the boil again and simmer for about 2 minutes. Stir the starch and 3 tbsp. water until smooth and thicken the sauce. Pour the sauce into previously rinsed hot glasses, close them tightly, turn them upside down for about 1 minute and let them cool down. The sauce can be kept in the refrigerator for about 1 month.