Last of Marmite used in quick spread (5)
I believe the answer is:
feast
'spread' is the definition.
(I've seen this before)
'last of marmite used in quick' is the wordplay.
'last of' suggests the final letters.
'used in' means one lot of letters goes inside another.
'quick' becomes 'fast' ('fast' can be similar in meaning to 'quick').
The final letter of 'marmite' is 'e'.
'e' placed into 'fast' is 'FEAST'.
(Other definitions for feast that I've seen before include "'Enough is as good as a .....'" , "Lavish meal" , "Banquet or religious festival" , "Grand meal" , "Saint's day, for example" .)