Meal is excellent with one portion doubled up (6)
I believe the answer is:
supper
'meal' is the definition.
(I know that Supper is a type of meal)
'excellent with one portion doubled up' is the wordplay.
I cannot really understand how this works, but
'portion' could be 'upper' (upper is a kind of portion) and 'upper' is found in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'is' is the link.
Can you help me to learn more?
(Other definitions for supper that I've seen before include "consumer" , "Light evening meal" , "Eats late" , "singing for this?" , "Evening repast" .)