Pine over a model recalled in a written study (8)
I believe the answer is:
treatise
'a written study' is the definition.
(I've seen this before)
'pine over a model recalled in' is the wordplay.
'pine over' becomes 'tree' (I can't explain this - if you can you should give a lot more credence to this answer).
'model' becomes 'sit' (e.g. for a painting).
'recalled' says the letters should be written in reverse.
'in' means one lot of letters goes inside another.
'sit' backwards is 'tis'.
'a'+'tis'='atis'
'tree' placed around 'atis' is 'TREATISE'.
Can you help me to learn more?
(Other definitions for treatise that I've seen before include "formal document" , "Disquisition" , "Systematically-written formal piece" , "Written study" , "Essay on theme" .)