The most common and most likely answer to this crossword clue is the 8 plus 9 letter word DEATHÂ BY CHOCOLATE
I've seen this crossword clue in The Guardian
D
E
A
T
H
Â
B
Y
C
H
O
C
O
L
A
T
E
Buddy explains!
The straight part
We know that "Might it be one’s ultimate dessert" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case might it be one’s ultimate dessert = death by chocolate.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.