Tasty underdone morsel (7)
I believe the answer is:
rarebit
'tasty underdone morsel' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Maybe you can see an association between them that I can't see?
'underdone morsel' is the wordplay.
'underdone' becomes 'rare' (synonyms).
'morsel' becomes 'bit' (synonyms).
'rare'+'bit'='RAREBIT'
Can you help me to learn more?
(Other definitions for rarebit that I've seen before include "Melted cheese with ale on toast" , "Simple dish" , "Dish of grilled cheese on toast" , "which the Welsh take down?" , "Cooked cheese on toast" .)