Part of book about Old Testament food (6)
I believe the answer is:
potage
'food' is the definition.
(I know that potage is a type of soup)
'part of book about old testament' is the wordplay.
'part of book' becomes 'page' (a page in a book).
'about' indicates putting letters inside.
'old testament' becomes 'ot'.
'page' going around 'ot' is 'POTAGE'.
(Other definitions for potage that I've seen before include "> sort of liquid nourishment" , "Thick, often creamy soup" , "this spoon-fed?" , "which is fairly thick" , "French soup, usually thick" .)