What does the cryptic crossword clue "Detention is like the topping on a dessert, you might say! (7)" mean?

The definition is "say!". The wordplay uses a homophone (sounds like). Sounds something like (you might say) ‘custardy’ The answer is CUSTODY.

Detention is like the topping on a dessert, you might say! (7)

Guardian Cryptic #28988 | 22 Across | 2023-02-08 flower