Indonesian food is varied and generally wonderful, though in out of the way spots like Pulau Banyak, off the West coast of Aceh, the choice for travelers is not extensive. I eat whatever is on offer on any given day at the one food stall in town — usually indeterminate fish in a yellowish or a reddish gravy. Yesterday the gravy was yellowish, and the first mouthful took me back to my grandmother’s kitchen. I was eating clam, of a…