How to make softer biscotti?
My kids love a similar recipe, but they also like them softer. What I do is reducing the second baking time by half.
Be aware that the shelf life of the biscotti is also reduced! ... Not a problem in my case since they don't survive more than two days ...
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Some history:

Though modern biscotti are associated with the Tuscan region of Italy, the popular Italian cookie traces its origins to Roman times. The word biscotto derives from “bis,” Latin for twice, and “coctum” or baked (which became “cotto,” or cooked). The Roman biscotti were more about convenience food for travelers rather than a pleasurable treat for leisurely diners. Unleavened, finger-shaped wafers were baked first to cook them, then a second time to completely dry them out, making them durable for travel and nourishment for the long journeys—Pliny boasted that they would be edible for centuries. Biscotti were a staple of the diet of the Roman Legions.
After the fall of the Roman Empire in 455 C.E, the country was repeatedly sacked by the Visigoths, the Vandals and others. The people did their best to survive; there was no culinary development. But with the Renaissance, cuisine also flowered. Biscotti re-emerged in Tuscany, credited to a Tuscan baker who served them with the local sweet wine. Their dry, crunchy texture was deemed to be the perfect medium to soak up the wine (and how much more flavorful than dunking a donut in coffee!). Centuries later, many still agree that dipping biscotti into Vin Santo is a perfect way to end a meal, or to while away an hour at a café.