Key to how the German made soup (7)
I believe the answer is:
chowder
'soup' is the definition.
(I've seen this before)
'key to how the german' is the wordplay.
'key to' becomes 'c' (I've seen this in other clues).
'the german' becomes 'der' ('the' in German).
'c'+'how'+'der'='CHOWDER'
'made' acts as a link.
(Other definitions for chowder that I've seen before include "clammy" , "possible first course?" , "Thick seafood soup" , "dish in America" , "Rich soup with fish, clams etc." .)