First, collect and measure all the required ingredients according to the ingredient list.
Combine soy sauce, Mirin, sugar, and sake in a small saucepan.
Stir well to dissolve the sugar completely.
Bring the mixture to a gentle boil over medium heat.
Lower the heat and simmer for 10 – 15 minutes until slightly thickened.
Remove from heat and let it cool; the sauce will thicken more as it cools.
Serve the eel sauce with sushi, grilled fish, meat, or vegetables.
Store in a clean airtight glass jar or bottle in the refrigerator.
