In a medium saucepan, combine the chopped jaggery and Vegetarian Dashi or stock over medium heat.
Stir continuously until the sugar is completely dissolved.
Add the sake to the saucepan and bring the mixture to a gentle simmer. Allow it to simmer for about 15 minutes, or until it has reduced by approximately ¼ cup / 65 ml. (2.2 fl oz)
Stir in the soy sauce and continue to simmer for 10 more minutes. Be careful not to let the mixture come to a rolling boil.
Remove the sauce from the heat and allow it to cool completely to room temperature. The sauce will thicken significantly as it cools.
Once cooled, transfer the Vegetarian Eel Sauce to an airtight jar or bottle and store it in the refrigerator.