Ensure that you’re using dashi granules, not already dissolved dashi.

If you do not have cornstarch use potato starch instead.

Store the eel sauce in the refrigerator and use it within 5 days. It may become even thicker as it’s chilled.

If you don’t want to use rice vinegar, you can substitute dry sherry, sweet marsala wine, or dry white wine.

For example, for a thin sauce, turn off the heat as soon as the sugar dissolves. For a thicker sauce, simmer it for 10 to 20 minutes.

Store the eel sauce in the refrigerator and use it within 5 days.