Dessert, for the most part, is tart (6)
I believe the answer is:
harlot
'is tart' is the definition.
(I've seen this in another clue)
'dessert for the most part' is the wordplay.
'dessert for' becomes 'harl' (I am not sure about this - if you are sure you should believe this answer much more).
'the most' means to remove the first letter.
'part' becomes 'pot' (pot is a kind of part).
'pot' with its first letter taken away is 'ot'.
'harl'+'ot'='HARLOT'
Can you help me to learn more?
(Other definitions for harlot that I've seen before include "woman like Rahab?" , "base" , "Call girl" , "Lady of the night" , "Prostitute" .)