It's apples when mixed with soup ingredients (5,4)
I believe the answer is:
split peas
'soup ingredients' is the definition.
(I've seen this in another clue)
'it's apples when mixed' is the wordplay.
'when mixed' is an anagram indicator.
'its'+'apples'='itsapples'
'itsapples' anagrammed gives 'SPLIT PEAS'.
'with' is the link.
(Other definitions for split peas that I've seen before include "What's in the soup" , "Dried vegetables" .)