Break up vessels (4)
I believe the answer is:
pans
'vessels' is the definition.
(I've seen this in other clues)
'break up' is the wordplay.
'break' becomes 'snap' (snapping is a kind of breaking).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'snap' written backwards gives 'PANS'.
(Other definitions for pans that I've seen before include "kitchen equipment" , "vessels" , "Kitchen utensils" , "Cooking utensils" , "roasts" .)