The most common and most likely answer to this crossword clue is the 12 letter word ROMANTICALLY
I've seen this crossword clue in The Guardian
R
O
M
A
N
T
I
C
A
L
L
Y
Buddy explains!

The straight part
We know that "with passion" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with passion = romantically.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.
What does ROMANTICALLY mean?
ROMANTICALLY adverb- In a romantic way.