This sounds so much like something I know as tapioca (Never heard of "sago.") ... that I went to see if it was the same thing by a different name. They're similar (says the internet), but not the same. They come from different plants, but in many recipes, they're interchangeable. I'll have to see if I can find this. It sounds very interesting -- and like something I had once in an Indonesian restaurant ... which I thought was just a specialized kind of tapioca.

Now, of course, you have me hankering to make tapioca pudding. You're devious that way. Don't think I don't know it.