Cooked in hot liquid, layer containing grease (6)
I believe the answer is:
boiled
'cooked in hot liquid' is the definition.
'boiled' can be an answer for 'cooked' (boiling is a kind of cooking). I'm not certain of the 'in hot liquid' bit.
'layer containing grease' is the wordplay.
'layer' becomes 'bed' (bed is a kind of layer).
'containing' is an insertion indicator.
'grease' becomes 'oil' (I've seen this before).
'bed' enclosing 'oil' is 'BOILED'.
Can you help me to learn more?
(Other definitions for boiled that I've seen before include "Cooked in hot water" , "Heated to point at which vapour forms" .)