Observe the stew? (6)
I believe the answer is:
seethe
'stew?' is the definition.
(I've seen this in another clue)
'observe the' is the wordplay.
'observe' becomes 'see' (observe can mean to see something).
'see'+'the'='SEETHE'
(Other definitions for seethe that I've seen before include "Bubble, almost boil" , "Bubble away" , "Boil, be turbulent" , "froth" , "Simmer with anger" .)