Seed cake

Seed cake was a type of cake found in Victorian Yorkshire.

Shortly before her death in 1893, Winifred Gillyflower offered the Eleventh Doctor seed cake, which he quickly declined. (TV: The Crimson Horror)

Behind the scenes
Though unremarked in the episode, the seed in question would almost certainly have been caraway, as the most common British meaning for "seed cake" is a "caraway seed cake".