Chocolate: one hardened in minute (8)
I believe the answer is:
noisette
'chocolate' is the definition.
(I've seen this before)
'one hardened in minute' is the wordplay.
'one' becomes 'i' (Roman numeral).
'hardened' becomes 'set' (synonyms).
'in' indicates putting letters inside.
'minute' becomes 'note' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i'+'set'='iset'
'iset' going inside 'note' is 'NOISETTE'.
Can you help me to learn more?
(Other definitions for noisette that I've seen before include "Rolled piece of lamb; nutty sweet" , "Flavoured with hazelnuts, chocolate, say" , "Small round cut of meat" , "Some rolled meat" , "Small piece of boneless lamb" .)