Grass Jelly

Method

1. Put 15 g of dried grass jelly herb in a bowl of cold water and rub it with your hands, changing the water two or three times until it runs clear of grit and dust. Drain, and snip or tear any long woody stalks in half so they fit the pan.
2. Tip the washed herb into a medium saucepan with 500 ml of water and 0.25 tsp of bicarbonate of soda, which draws the gel out of the leaves. Bring to the boil over high heat, then lower to a bare simmer, cover, and cook 1 hour 10 minutes. Check every 20 minutes and add a splash of boiling water if the leaves start to sit above the liquid.
3. Strain the brew through a fine sieve lined with muslin set over a jug, pressing hard on the leaves with the back of a ladle to squeeze out every drop of the slippery liquid, then discard the leaves. You should have a dark, almost black, faintly viscous liquid; make it up to 350 ml with hot water if you are short.
4. Whisk 15 g of tapioca starch with 3 tbsp of cold water until completely smooth with no lumps. Return the strained liquid to the rinsed pan and bring it back to a gentle boil over medium heat.