The Etymology of Biscotti
Biscotti is the Italian plural of biscotto, and both descend from Medieval Latin biscoctus — bis (twice) plus coctus (cooked, past participle of coquere, to cook). The twice-baking technique was a preservation method long before refrigeration: a loaf was first baked, sliced, then returned to the oven to drive out remaining moisture, leaving a hard rusk that kept for weeks at sea or on military campaign. Roman legions carried biscoctus, and so did medieval pilgrims and sailors. The Tuscan town of Prato turned the technique into a delicacy — cantucci di Prato, almond-studded biscotti dipped into vin santo — by the 14th century. English already had biscuit (same root, French route) since the 14th century, so when biscotti arrived in the late 19th century with Italian café culture, it was kept in its Italian plural form to mean the harder, almond-rich Italian version. German Zwieback (twice-baked) and Spanish bizcocho carry the same Latin idea.