Bring water to simmer, add tamarind and allow to steep for 30 minutes, strain, and reduce water to 1/5 of original quantity (400 g).

In saucepan over medium heat, caramelize palm sugar with water to dark amber color.

Add tamarind water reduction, apple cider vinegar, fish sauce, ginger, garlic, black peppercorn, reduce heat to very low, continue reduction for 30 more minutes or until tare is syrup consistency, remove from heat, add dark soy.

Pass through fine mesh strainer, discard ginger and peppercorns, reserve in storage containers, chill to room temperature, then transfer to cooler.