Yolk

The yolk of an egg, or egg yolk, was yellow. (PROSE: Verdigris) It was differentiated from other parts of the egg, such as the egg whites (PROSE: The Man from DOCTO(R)) and the eggshell, (PROSE: The Man from DOCTO(R), The Death of Me) by often being quite runny. (PROSE: Totem, The Death of Me)

The Sixth Doctor found that a good boiled egg was one whose yolk was not too runny, and not too hard. The eggs served at Chloe and Arthur's bed and breakfast, he decided, were expertly made. (PROSE: The Death of Me)

When eating boiled eggs, if one was not careful, they might break the eggshell too forcefully, and so potentially get a yolk stain on their clothing. (PROSE: The Death of Me)

Poached eggs could have a runny yolk. (PROSE: Policy to Invade)

The Peladon equivalent of bacon and eggs included runny egg yolk, which trickled out the corner of Damakort's mouth. (PROSE: Legacy)

A Crème Brulée was made from blended cream and egg yolk, flavoured with vanilla, almonds or bitter chocolate, and covered in brown sugar. (PROSE: Earth)