Long live supermarket with only one American potato (7)
I believe the answer is:
vivaldi
'long live' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'supermarket with only one american potato' is the wordplay.
'supermarket' becomes 'Aldi' (German supermarket also operating in the UK).
'with' says to put letters next to each other.
'only one american potato' becomes 'viv' (I can't explain this - if you can you should believe this answer much more).
'aldi' after 'viv' is 'VIVALDI'.
Can you help me to learn more?
(Other definitions for vivaldi that I've seen before include "Italian composer of 'The Four Seasons'" , "Italian composer (the Red Priest) , d.1741" , "Italian composer, Antonio (d. 1741)" , "Italian composer known as "the red priest"" , "Venetian composer ("The Red Priest"), d. 1741" .)