From Frankish *blank (white) via Old French—originally to whiten almonds by boiling off their skins.
To briefly immerse food in boiling water, then in cold water, to soften, peel, or preserve color; also, to turn white from shock.
From Old French 'blanchir' (to make white), from 'blanc' (white), from Frankish *blank (white, shining). The cooking sense comes from blanching almonds—boiling them to slip off the brown skin and reveal the white nut beneath. Key roots: *blank (Frankish/Germanic: "white