I really put the sauce away in elementary form (7)
I believe the answer is:
isotope
'elementary form' is the definition.
'i really put the sauce away' is the wordplay.
'really' becomes 'so' (both can mean 'extremely').
'put the sauce away' becomes 'tope' (archaic term meaning to drink alcohol or 'sauce').
'i'+'so'+'tope'='ISOTOPE'
'in' is the link.
(Other definitions for isotope that I've seen before include "elementary variation in it" , "Oops, tie up the atom" , "Atomic stuff" , "Distinct form of an element" , "Variant element form" .)