Curiously enough, the word biscotti was not borrowed into English until the late 1980s, when it was adopted as the plural of Italian biscotto (so, technically, a biscotti is incorrect; it should be a biscotto). Meanwhile, the word biscuit, which has been around for far longer, came from the French word bescuit. It was borrowed in the 12th century and took the form bisket for a while, until people decided they wanted to return to the French roots of the word. Both of these are from the same etymon: Latin biscoctum, which meant "twice cooked". This particular definition was applied because biscuits and biscotti in the old times were baked twice in two separate ovens. Biscotum is composed of the prefix bis-, meaning "two" (it's a lesser known variant of bi-, coming from Proto-Indo-European dwis, with the same meaning), and coctus, which is a conjugation of coquere, meaning "to cook" or "ripen". The latter, through Proto-Italic keko, comes from PIE pek, also with the same definition.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.