The cookie, made specifically for the Nimrod Expedition (1907-1909), is a Huntley & Palmers biscuit that measures 3 inches (7.7 cm.) in diameter and is fortified with milk protein. No word on how it tastes — stale, presumably — after all these years.
The sale price was £250 (~$390) short of the highest estimate. Perhaps, not many people want a century-old cookie.