Infallible dessert, with a measure of alcoholic content (9)
I believe the answer is:
foolproof
'infallible' is the definition.
(similar in meaning)
'dessert with a measure of alcoholic content' is the wordplay.
'dessert' becomes 'fool' (type of dessert).
'with' is a charade indicator (letters next to each other).
'a measure of alcoholic content' becomes 'proof' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'fool'+'proof'='FOOLPROOF'
Can you help me to learn more?
(Other definitions for foolproof that I've seen before include "Not liable to failure" , "tried and tested" , "Certain" , "Can't be misinterpreted, even by simpleton" , "sure to work" .)