Theme involves recipe for a certain degree of latitude? (6)
I believe the answer is:
tropic
'a certain degree of latitude?' is the definition.
(eg Tropic of Cancer is at a certain latitude)
'theme involves recipe' is the wordplay.
'theme' becomes 'topic' (synonyms).
'involves' is an insertion indicator.
'recipe' becomes 'r' (abbreviation).
'topic' going around 'r' is 'TROPIC'.
'for' acts as a link.
(Other definitions for tropic that I've seen before include "Particular latitude" , "Latitude associated with Capricorn or Cancer" , "eg Capricorn" , "One of two parallels of latitude" , "Capricorn, say" .)