well, literally biscotti means twice-cooked, 'bis' meaning twice or second and 'cotti' being the plural for the adjective 'cooked'. so twice cooked. but why? the first thing to note is that traditionally italian cookies are not soft, but hard. (biscotti in italy refers to cookies in general, while outside of italy they generally refer to the specific cantuccini di prato cookies) crumbliness being a separate factor in the sense that all cookies are hard but some are also crumbly. italians refer to how much something is 'friabile' or how easily it crumbles. a good pasta frolla cookie (or a good frolla pie crust) should be hard but also crumbly. while cantuccini biscotti are generally less crumbly and really hard. this means that home made cookies or biscotti are almost always baked until the last moment before they start to take a burnt flavour. the outside of the cookie tends to be heavily coloured/caramelized. industrial cookies tend not to be coloured, better temperature control and baking procedures allow them to produce uncoloured, yet hard and crumbly cookies. they are almost invariably very dry. although this is not seen as a fault. instead a grave fault in a cookie is if it is soft, which either signifies a not properly cooked cookie(interesting to note that in english cookie also derives from the verb 'to cook'!) or a cookie that has become stale and absorbed to much humidity. it makes sense that in the old days cookies would be produced this way. as a dry cookie could be stored much longer without going off. (humidity=bacteria,mold etc). nowadays cookies can be baked and produced solely for daily consumption or stored under vacuum packing, which allows for soft baked cookies. but i am rambling..
so basically no half-baked, no soft-baked cookies. i remember several months ago buying a pack of pepperidge farm cookies at one of the bigger super markets here. and when trying this pack of cookies with friends over a coffee break, we all at first thought that the packaging had broken and the cookies had gone off!! and i used to like soft-baked cookies...
i had just... forgotten..!
anyways, back to the original question. why twice baked? twice baking is the traditional method for cantuccini cookies. once to get the colour on the outside of the cookie roll, then a second time after they are sliced and placed on there sides to finish baking. similarly i'm guessing that cookies in the old days, with ovens whose temperatures must have been difficult to control and cookies being as small as they are, were always twice baked. once at higher temperature and then at a lower temperature to ensure that the cookie was completely cooked.
more than all that, biscotti also play an important cultural role. they accompany most breakfasts at home. breakfast being a cup of coffee and milk and some biscotti cookies. finished. no eggs, no bacon. nothing salty and not too much. the first time I ate eggs for breakfast, sharing a flat with italians they looked at me like i was an alien. i think the accompanying coffee was particularly offensive. I've managed to ween myself from my old habits. now eggs for breakfast seem even a little strange to me... as do soft cookies.
that, more or less, is what biscotti means.