Round tamale that’s mixed up milled grain (7)
I believe the answer is:
oatmeal
'milled grain' is the definition.
'round tamale that's mixed up' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'that's mixed up' indicates an anagram.
'tamale' anagrammed gives 'atmeal'.
'o'+'atmeal'='OATMEAL'
(Other definitions for oatmeal that I've seen before include "Ground grain used to make porridge" , "Porridge constituent" , "Kind of porridge" , "ground food!" , "The material for porridge" .)