Boiling broth requires pulse (5)
I believe the answer is:
throb
'pulse' is the definition.
(I know that pulse can be written as throb)
'boiling broth' is the wordplay.
'boiling' indicates an anagram.
'broth' with letters rearranged gives 'THROB'.
'requires' acts as a link.
(Other definitions for throb that I've seen before include "Strong rhythmic beat" , "Pulse" , "Have strong or irregular heartbeat" , "Beat quickly from excitement etc" , "Broth (anag.)" .)