The most common and most likely answer to this crossword clue is the 8 letter word BAKEWELL
I've seen this crossword clue in Financial Times
B
A
K
E
W
E
L
L
Buddy explains!
The straight part
We know that "What decent pastrycooks do/town famous for tart" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what decent pastrycooks do/town famous for tart = bakewell.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.