Tart left devotee outside (4)
I believe the answer is:
flan
'tart' is the definition.
(I've seen this before)
'left devotee outside' is the wordplay.
'left' becomes 'l' (common abbreviation).
'devotee' becomes 'fan' (synonyms).
'outside' indicates putting letters inside.
'l' inserted inside 'fan' is 'FLAN'.
(Other definitions for flan that I've seen before include "dish, sweet or savoury" , "Sweet/savoury open tart" , "Open pastry dessert" , "Open-topped pie" , "Quiche" .)