Supplier's broth is nutritional at the core (8)
I believe the answer is:
stockist
'supplier's' is the definition.
(stockist is a kind of supplier)
'broth is nutritional at the core' is the wordplay.
I cannot quite see how this works, but
'broth' could be 'stock' (synonyms) and 'stock' is found in the answer.
'is' is found in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stockist that I've seen before include "Retailer of a particular line of goods" , "Shop that carries a particular item" , "Retailer carrying a particular item" , "dealer" .)