Xiancao Dong (Grass Jelly)

Instructions

1. Snip the dried mesona into 4-inch (10 cm) lengths and rinse it in several changes of water until no grit remains.
2. Bring the 2000 ml water to a boil in a large pot, add the mesona and baking soda, and simmer, partly covered, stirring now and then, until the liquid is very dark and slightly slick, about 1 hour.
3. Strain the tea through a sieve lined with fine cloth, pressing on the herb, then strain it a second time. Measure it: you need 1.2 L. Boil it down if there is more, or add water if there is less.
4. Return the tea to the pot, add the rock sugar and bring back to a simmer, stirring until dissolved, about 3 minutes.
5. Stir the sweet potato starch into the cold water until smooth. Pour it into the simmering tea in a thin stream while stirring, then keep stirring until the mixture thickens, turns glossy and bubbles, 2 to 3 minutes.
6. Pour into the square dish. Cool at room temperature for 1 hour, then refrigerate until firm, about 3 hours.
7. While the jelly chills, simmer the dark brown sugar and the 100 ml water in a small pan until syrupy, about 3 minutes, then cool completely, about 20 minutes.
8. Cut the jelly into 3/4-inch (2 cm) cubes and divide among 6 bowls. Spoon over the brown sugar syrup and the evaporated milk and serve cold.