The most common and most likely answer to this crossword clue is the 6 letter word GELATI
I've seen this crossword clue in Financial Times
G
E
L
A
T
I
Buddy explains!
The straight part
We know that "refresher courses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case refresher courses = gelati.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 GELATI mean?
GELATI noun- Gelato, Italian style ice-cream; a serving of gelato, often in a cone.
- An Italian variant of ice cream made from milk and sugar, combined with other flavourings. The ingredients are supercooled while stirring to break up ice crystals as they form.