The two consuming starter of rich soup (5)
I believe the answer is:
broth
'soup' is the definition.
(broth is a kind of soup)
'the two consuming starter of rich' is the wordplay.
'the two' becomes 'both' (synonyms).
'consuming' is an insertion indicator.
'starter of' indicates taking the first letters.
The first letter of 'rich' is 'r'.
'both' enclosing 'r' is 'BROTH'.
(Other definitions for broth that I've seen before include "Thin soup" , "Type of soup" , "Kind of soup" , "Stock" , "Setting for culture" .)