Don’t split up tasty fragments! (4,3)
I believe the answer is:
stay put
'don't split' is the definition.
'up tasty fragments' is the wordplay.
'fragments' indicates an anagram.
'up'+'tasty'='uptasty'
'uptasty' is an anagram of 'STAY PUT'.
(Other definitions for stay put that I've seen before include "Remain in place, don't move" , "Stick around" , "Remain in one place" , "Informally, don't move - remain in situ" , "Remain unmoving" .)