The most common and most likely answer to this crossword clue is the 7 plus 2 plus 8 letter word PARSLEY IS GHARSLEY
I've seen this crossword clue in The Guardian
P
A
R
S
L
E
Y
I
S
G
H
A
R
S
L
E
Y
Buddy explains!
The straight part
We know that "6 complains about cooking ingredient" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case 6 complains about cooking ingredient = parsley is gharsley.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.