They are actually quite easy to make, but they need to sleep about half a day (or night) before they can be grilled.
They are very satisfying to bite into and for some reason, they actually, really give a cooling sensation in the mouth. Unlike 羊羹, they can't be chilled (葛 doesn't like that, it'll turn rubbery), so the effect is quite noticeable!
Recipe
100 gr 葛 flour
200 gr sugar
400 gr water
150 gr luke-warm water
上新粉 for dusting
Method
It can look a bit one dimensional, so most variations use two different colours that are just barely mixed. This looks very pretty when cut! So divide ingredients in half.
Mix sugar and 葛, add water and mix. Sieve, then heat until sticky.
Into the warm water, add the food colouring and add it in little steps to the sticky dough until incorporated (that's the TT method. Other videos don't bother with that.)
Add the two colours into the 流し器 and just barely mix (TT mixes it in the pot, but I find it easy to overmix that way)
Steam the whole affair for 10' under a cloth-lined lid.
Take out, cover with a moist, cool cloth and let it cool on the counter (not the fridge!) for half a day
Then powder with 上新粉, upend and let fall out. More 上新粉, then cut. It makes a big difference if you manage to cut them straight, so using a string to cut might be a good idea here.
Cover all sides with 上新粉, brush away excess and grill in Teflon until slightly firmed. For me, that was about 45 seconds per side on 6.
👆 I wonder if adding a little bit of sugar to the 上新粉 could give a bit of a caramelised surface and a more satisfying bite?
They can be brandied afterwards with butterflies, for example, or water patterns.