Drink best topping (6,5)
I believe the answer is:
double cream
'topping' is the definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'drink best' is the wordplay.
'drink' becomes 'double' (double shot of alcohol).
'best' becomes 'cream' (both can mean the elite).
'double'+'cream'='DOUBLE CREAM'
Can you help me to learn more?
(Another definition for double cream that I've seen is " fat and thick".)