"there is a relationship with biscotto = bis - cotto ( cookie) which literally means cooked twice."

Like "Zwieback", which means exactly the same in German. And biscuit. The interesting thing is, and here we are back at clay again, is that in Britain, pottery that has been through the first firing (necessary before the application of glaze) is called "biscuit ware" ("bisque" in North America), even though it's been baked only once. I assume they're using the word "biscuit" to refer to the hardness, rather than how many times it's been baked.