Abrupt way to stop using Christmas leftovers? (4,6)
I believe the answer is:
cold turkey
'abrupt way to stop' is the definition.
(as in going cold turkey when quitting drugs)
I can't explain the rest of the clue.
(Other definitions for cold turkey that I've seen before include "Quick way to come off horse" , "When horse perhaps barred" , "Depression" , "result of stopping drugs" , "Cure" .)