Turkey that's dandy stuffed with last of offal (4)
I believe the answer is:
flop
'turkey' is the definition.
(I've seen this before)
'dandy stuffed with last of offal' is the wordplay.
'dandy' becomes 'fop' (synonyms).
'stuffed with' means one lot of letters goes inside another (some letters get stuffed inside).
'last of' indicates one should take the final letters.
The last letter of 'offal' is 'l'.
'fop' going around 'l' is 'FLOP'.
'that's' acts as a link.
(Other definitions for flop that I've seen before include "Community cards in poker" , "Utter failure" , "turkey" , "Fall limply - box-office failure" , "crash" .)