I have never successfully used either of these but according to Mors Kochanski's "Northern Bushcraft" (or just "Bushcraft" in the second edition), there are (at least) two types of Tinder Fungus - False Tinder Fungus (which is what you're describing) and True Tinder Fungus. True Tinder Fungus, which I believe is found only on living birch trees, looks like a black diamond-shaped growth on the bark of the tree and only needs to be dried. The False Tinder Fungus, which looks like the front part of a horse's hoof sticking out of the trunk, is much more common, but needs to be prepared in advance as you describe. Mors Kochanski recommends boiling it in a slurry of wood ash. (Not the whole fungus; the "amadou" is actually the suede-like inner skin of the fungus, and that is what is extracted and used to prepare the tinder.)