A soufflé was a baked cake which required, amongst other ingredients, eggs and milk. Ellie Oswald always said that "a soufflé isn't a soufflé; a soufflé is a recipe."
Her daughter, Clara Oswald, attempted to make soufflés on multiple occasions, but to no avail. She was not, unfortunately, very skilled at soufflé-making, as she burnt them and otherwise couldn't get them to rise properly. She hoped to one day be "soufflé girl". (TV: The Name of the Doctor)
After having entering the Doctor's time stream and getting split up into multiple forms across time and space, Clara, in her Victorian life, asked for a kitchen upon first arrival in the Doctor's TARDIS, as she wished to make soufflés. (TV: The Snowmen)
While under the name Oswin Oswald in the Dalek Asylum, she claimed to be have been fighting the Daleks by making soufflés. While in this life, she did gain the nickname "soufflé girl". The Eleventh Doctor — suspicious of where she could possibly be getting the milk and eggs for these creations — eventually determined that she was, in reality, making no such dishes. She was merely sublimating the terrible truth that she had been converted into a Dalek, and was hallucinating the soufflés, along with her perceived environment. (TV: Asylum of the Daleks)
In the 1970s, Delia Smith appeared in an episode of The Scorchies Show and baked a soufflé. The Third Doctor's companion Jo Grant particularly enjoyed this episode. (AUDIO: The Scorchies)
The Fourth Doctor regretted losing the ability to make successful soufflés after his most recent regeneration. (PROSE: Heart of TARDIS)