Super food supplied endlessly: that's the stuff (6)
I believe the answer is:
fabric
'the stuff' is the definition.
(I've seen this before)
'super food supplied endlessly' is the wordplay.
I cannot really see how this works, but
'super' could be 'fab' (short for fabulous) and 'fab' is found in the answer.
The remaining letters 'ric' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for fabric that I've seen before include "(Texture of) cloth" , "Perhaps felt" , "'Cloth, textile (6)'" , "Underlying structure" , "Material in general" .)