6 tbsps soy sauce
4 tbsps mirin
2 tbsps brown sugar (or caramelized sugar syrup)
dash of rice wine vinegar
Recipe
To make the eel sauce: Combine ingredients in a small saucepan and bring to boil. Let boil for a minute or so and reduce to simmer until slightly thickened. Let cool (it will thicken some more, so don’t boil it down too much).