Marcel chewed over a toffee (7)
I believe the answer is:
Here is my best explanation:
'toffee' is the definition.
(I've seen this before)
'marcel chewed over a' is the subsidiary indication.
'chewed' is an anagram indicator.
'over' indicates putting letters inside.
'marcel' is an anagram of 'carmel'.
'carmel' placed around 'a' is 'caramel'.
(Other definitions for caramel that I've seen before include "Toffee", "Brown", "Sugar solution heated till brown", "Dark brown substance", "Browned syrup", "Soft toffee", "chewy sweet", "Shade", "Soft sweet" and "Chewy sweet - burnt sugar".)