Pickled onion
From Tardis Wiki, the free Doctor Who reference
Pickled onions were a prepared food found on Earth. (TV: World War Three, AUDIO: Invasion of the Daleks)
Mickey Smith had pickled onions (along with pickled eggs and gherkins) in his cupboard. Jackie Tyler used them to kill a Slitheen. The vinegar (and therefore the acetic acid) they were pickled in could dissolve a Raxacoricofallapatorian's calcium-based physiology. (TV: World War Three)
Susan Mendes's grandmother sent her pickled onions from Earth in 4162. She also left a jar of them for Alby Brook. (AUDIO: Invasion of the Daleks)
