The most common and most likely answer to this crossword clue is the 3 plus 4 plus 7 letter word OFF YOUR TROLLEY
I've seen this crossword clue in Financial Times
O
F
F
Y
O
U
R
T
R
O
L
L
E
Y
Buddy explains!
The straight part
We know that "What you serve/nuts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what you serve/nuts = off your trolley.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.