Ace Frenchman in clear prepared sweet (7)
I believe the answer is:
caramel
'sweet' is the definition.
(caramel is a kind of sweet)
'ace frenchman in clear prepared' is the wordplay.
'ace' becomes 'a'.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'in' indicates putting letters inside.
'prepared' is an anagram indicator.
'a'+'m'='am'
'clear' is an anagram of 'carel'.
'am' going within 'carel' is 'CARAMEL'.
(Other definitions for caramel that I've seen before include "Soft sweet" , "Sugar solution heated till brown" , "Dark brown substance" , "Chew candy" , "Browned syrup" .)