Jamu (Indonesian Turmeric Ginger Tonic)

Method

1. 1Peel the turmeric and ginger roots, then grate or thinly slice them. Turmeric stains everything it touches — cutting boards, fingertips, countertops — so work on a surface you don't mind discoloring, or wear gloves. If your palm sugar comes as a block, shave or chop it finely so it dissolves quickly. If using lemongrass, bruise the stalk with the back of a knife to release its oils.
2. 2Bring the water to a boil in a medium saucepan. Add the turmeric, ginger, tamarind paste, palm sugar (unless you are sweetening with honey), salt and the lemongrass if using, and stir until the sugar has dissolved and the tamarind has broken up. Reduce the heat to a gentle simmer and cook uncovered for 10 to 15 minutes. The liquid will turn a deep golden-orange. Don't cut this short: this is how kunyit asam is made in Indonesia, with everything boiled together, and the full 10 minutes is what brings the flavors together.
3. 3Take the saucepan off the heat and taste. The tamarind should give a clear sourness against the earthy turmeric: if the drink tastes flat, stir in a little more tamarind; if it is too sharp, a little more palm sugar. If you are using black pepper, add it now. If you are sweetening with honey instead of palm sugar, don't boil it: stir in about 45 g at this point.
4. 4Let the mixture steep for 5 minutes, then strain it through a fine-mesh sieve or cheesecloth into a clean pitcher, pressing on the solids to extract every drop of flavor. Discard the pulp. If using coconut oil, stir it in now.
5. 5Serve the jamu warm in cups, or let it cool to room temperature and pour it over ice. It keeps in the refrigerator for up to 3 days — shake or stir before serving, as the turmeric settles to the bottom.