Sourdough biscotti have been on my mind for a while, but they posed a bit of a challenge: with sourdough starter comes water, and extra water is not something that we usually want in any cookie dough, never mind biscotti. For these “twice-baked” cookies, the dough is formed into a log and partially baked, then sliced and baked again until dry. Extra water is just not helpful here.
The solution I came to, in addition to using a stiff (50%-hydration) starter, is to cut down on the sugar, which behaves very much like a liquid ingredient in a dough. (If you don’t believe me, try taking a basic unsweetened dough and mixing in a bunch of sugar; you’ll swear you just dumped a bucket of water in there.) So these have about 30% less sugar than you’ll see in many biscotti recipes, but interestingly, they taste plenty sweet to me. I would not market them as “diet biscotti.” They’re definitely dessert.
The dough is still plenty wet, and log-forming is a little tricky. I found a plastic dough scraper helpful to scrape up and shape and smooth the sides once the dough is on the parchment-lined pan. But even if you make your log nice and compact, it’s going to start flattening out before it even hits the oven, and after a few minutes in there will look like a praline on a hot New Orleans sidewalk. Don’t panic. It will rise (a little) and have a pretty good biscotti shape by the time it’s done.