Very happy to make broth (4)
I believe the answer is:
Here is my best explanation:
'broth' is the definition.
'very happy' is the wordplay.
'very' becomes 'so' (I've seen this in other clues).
'happy' becomes 'up' (I've seen this in other clues).
'to make' is the link.
(Other definitions for soup that I've seen before include "Liquid - course", "Developer", "Minestrone?", "liquid content in this food", "Preliminary course", "Liquid food", "Eg, potage, broth", "Eskimo people", "Photographic developer" and "Stolen plate melted down".)