Composer penning key scores (7)
I believe the answer is:
tallies
'scores' is the definition.
(I know this)
'composer penning key' is the wordplay.
I cannot really see how this works, but
'key' could be 'e' (a musical key) and 'e' is present in the answer.
'composer' could be 'tallis' (choral composer Thomas Tallis) and 'tallis' is found in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tallies that I've seen before include "Counts, of votes say" , "Matches, corresponds" , "Records" , "Recordings" , "Agrees; scores" .)