Bloomer spread with cheese and pickle tops posh filling (9)
I believe the answer is:
buttercup
'bloomer' is the definition.
(plant which blooms)
'spread with cheese and pickle tops posh filling' is the wordplay.
I cannot quite see how this works, but
'spread' could be 'butter' (butter is a spread) and 'butter' is found within the answer.
'posh' could be 'u' (abbreviation for upper-class - opposite to non-U) and 'u' is located in the answer.
This explanation may well be incorrect...
(Other definitions for buttercup that I've seen before include "weedy type" , "found in meadow" , "Meadow flower poisonous to cattle" , "growth in the field" , "Common yellow meadow plant" .)