Mary Berry (in-universe)

Mary Berry was a celebrity chef whom the Twelfth Doctor thought resembled his first incarnation; (PROSE: Twice Upon a Time) the Twelfth Doctor even referred to his earlier incarnation as Mary Berry, (TV: Twice Upon a Time) but the reference was lost on the First Doctor as he had yet to meet her, though eventually his third incarnation would spend a summer with her on a narrowboat in the Cotswolds. (PROSE: Twice Upon a Time)

Mary Berry attended the Twelfth Doctor's Christmas dinner party for Sprout Boy when he was feeling left out. She shared a Christmas cracker with John Luther. (TV: Sprout Boy meets a Galaxy of Stars)

Mary Berry assisted Eddie Redmayne when he contacted the Twelfth Doctor in the TARDIS. She acted as his personal cook. (TV: Looking for Pudsey)

Behind the scenes
Mary Berry portrayed herself in Looking for Pudsey.