Start out with a cracker of a plan (9)
I believe the answer is:
stratagem
'a plan' is the definition.
(stratagem is a kind of plan)
'start out with a cracker' is the wordplay.
'out with' indicates anagramming the letters (out can mean wrong or inaccurate).
'cracker' becomes 'gem' (I can't justify this - if you can you should believe this answer much more).
'start' anagrammed with 'a' gives 'strata'.
'strata'+'gem'='STRATAGEM'
'of' is the link.
Can you help me to learn more?
(Other definitions for stratagem that I've seen before include "Device" , "Clever scheme" , "Ploy - start game (anag)" , "Ruse" , "Plan to deceive enemy" .)