If you remember the post about Narcisses flowers you might remember the character 仙 which is composed of the two radicals 亻 (person) and 山 (mountain), which together means immortal. The character is used here again. The English name for 仙草 is "grass jelly" and is usually found as a black jelly-like treat that is usually cut up into little cubes. The herb that it is made from is indeed a plant, medicinal in this case, which is believed to have cooling properties when prepared in this way. From Wikipedia, "Grass jelly is made by boiling the aged and slightly oxidized stalks and leaves of Mesona chinensis1 (member of the 2mint family) with potassium carbonate for several hours with a little starch and then cooling the liquid to a jelly-like consistency.1 .... The jelly itself has a slight bitter taste, a light 3iodine and lavender flavor, and is a translucent dark brown or sometimes perceived to be black."
The Taiwan twist, and where 燒 comes in, is that it is re-cooked (or perhaps never cooled in the first place) and then served in a bowl with lots of sweet additions, usually beans, tapioca, and barley. As you will see in the video below, my 燒仙草 has, in the order taken:
紅豆 hong dou (lit. red bean), known as adzuki beans
地瓜 di gua (lit. earth melon)* sweet potato
大豆 da dou (lit. big bean) soybean**
綠豆 lu dou (lit. green bean) mung bean
粉圓 fen yuan (lit. powder ball) another name for the black tapioca balls that are in zhen zhu nai cha ("bubble milk tea")
湯圓 tang yuan (lit. soup ball), similar to fen-yuan but I think made from glutinous rice flour instead of tapioca
地瓜圓 di gua yuan (lit. earth melon ball), similar to tang yuan but made with sweet potato starch
芋圓 yu yuan (lit. taro ball), similar to di-gua-yuan but made with taro root starch
It's actually quite a medley of flavors and textures. It's more of a meal than a drink, I guess, and as it grows colder as you eat it, the xian-cao which started as a thick liquid begins to turn into a jello-like substance.
*other things that are a "gua" 瓜, melon, in Mandarin are watermelon, honeydew, papaya, cucumber, and gourds. I'm not sure what the classification standard is but I think it is the general oval shape with tapered edges that qualifies something as a "gua".
**what we think of as soybean is 黃豆 huang dou (lit. yellow bean) but apparently 大豆 also translates into soybean. I'm not sure what the difference is. Soy milk, "dou-jiang," and soy sauce are both made from huang dou. As far as I can tell, da dou looks similar to a kidney bean in size and color but not shape.