• 200 ml (7 fl oz) soy sauce (preferably shibanuma)
• 165 g

Pour the soy sauce into a small heavy-based saucepan and bring to the boil. Add the sugar and eel stock and stir until dissolved. Bring the liquid back to a simmer and reduce over medium–low heat for about 15 minutes, until the liquid thickens. Add the mirin and sake, and continue to reduce until thick and syrupy. Remove from the heat and leave to cool. Transfer to a container and refrigerate u