Come upon fatty spread — something I don't fancy (3,2,3,2,3)
I believe the answer is:
not my cup of tea
'something i don't fancy' is the definition.
(something not to someone's taste)
'come upon fatty spread' is the wordplay.
'spread' indicates an anagram.
'come'+'upon'+'fatty'='comeuponfatty'
'comeuponfatty' is an anagram of 'NOT MY CUP OF TEA'.
(Other definitions for not my cup of tea that I've seen before include "It doesn't appeal to me (3,2,3,2,3)" , "Far from a personal preference" .)