The most common and most likely answer to this crossword clue is the 9 letter word TRATTORIA
I've seen this crossword clue in The Guardian
T
R
A
T
T
O
R
I
A
More clues leading to the result TRATTORIA
- Even Mafia characters go off pastry served up here?
- Restaurant having upended dessert, a riot breaking out
- Shot traitor at restaurant
- Display unrestrained creative work over restaurant
- Restaurant offers excellent crumble, sweet course served retro-style
- Rock found in ideal pudding served up in restaurant
- Schooled trio at art courses offered here
- I go off pastry sent around by a restaurant
- Top-quality crumble and pastry rejected
- Current books on pastry standing in restaurant
Buddy explains!

The straight part
We know that "restaurant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case restaurant = trattoria.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 TRATTORIA mean?
TRATTORIA noun- A small, informal Italian-style restaurant.