I used to make biscotti very frequently. My favorite recipe called for butter (I kept trying to find one without, like true Italian biscotti, but alas, those never turned out well.)
I finally hit on a recipe, using toasted hazelnuts as the nut in them. I could not find hazelnut flavoring anywhere, so I used about 1½ T of hazelnut coffee syrup. It did a few things that improved my biscotti.
(My original recipe was very similar to Siduri's).
1. the small addition of liquid - very small - gave me more time "in the zone" the point where the biscotti slices easily. Before that I would wait a couple of minutes after the 1st baking and then slice. All went well until it cooled too much, then it crumbled. The very small addition of the syrup gave me more time.
2. the flavor, of course,
3. the cookies did not get brown too fast (we liked ours pale, like real Italian ones)
I always made a triple recipe - enough for 4 (large flat) logs on 2 large cookie sheets. (baked at the same time I never noticed a bit of difference baking them one at a time) My cookies were generously long, not the typical "home made" look.
When I took them out after the 1st baking, (when golden and holding their shape well) I let them set maybe 2-4 minutes, If you sliced them too soon, they mushed up when slicking, when they cooled too much, they crumbled. You had to hit it just at the right temperature. (As I mentioned above the small amount of liquid helped extend the period)
I remember they were still rather hot as I sliced, because I usually held the log with a dish towel while I worked. I used a serrated knife and used the knife edge to scoot them on the cookie sheet. I did NOT lay them on their sides. I merely spread them out all over the sheet with the knife behind them for support, that way the sides were exposed to the heat on the 2nd baking and I did not have to turn them. The knife helped keep them in shape when they were softer from the heat
On the 2nd baking, I put both pans back in the oven at reduced temperature. I cooked it for about 10-12 minutes, then I turned the oven off and left the cookies in until the oven was completely cool - usually overnight.
This worked beautifully for me, drying them out completely without over browning. The tiny bit of extra liquid helped me slice them cleanly and leaving them standing up eliminated turning them over. Also I found chopping the nuts to a small pea size, no larger, helped because when the knife it them it made a mess too.
Hope this helps