Bon vivant Elaine periodically eats overly good treat (9)
I believe the answer is:
epicurean
'bon vivant' is the definition.
(synonyms)
'elaine periodically eats overly good treat' is the wordplay.
'periodically' indicates alternate letters (letters must be selected 'every so often').
'eats' means one lot of letters goes inside another.
'overly good treat' becomes 'picure' (I can't explain this - if you can you should believe this answer much more).
The alternating letters of 'elaine' are 'ean'.
'ean' placed around 'picure' is 'EPICUREAN'.
Can you help me to learn more?
(Other definitions for epicurean that I've seen before include "enjoyer of fine food" , "Foodie's" , "expert on food" , "one sensuous and Greek" , "advocate of enjoyment" .)