Christian festival with man of the Bible going to church — what's on the menu? (5,5)
I believe the answer is:
white sauce
'what's on the menu?' is the definition.
(sauce that might be part of a meal)
'christian festival with man of the bible going to church' is the wordplay.
'christian festival' becomes 'Whit' (Whitsuntide).
'with' is a charade indicator (letters next to each other).
'man of the bible' becomes 'esau' (Esau is a figure from the Old Testament).
'going to' says to put letters next to each other.
'church' becomes 'CE' (abbreviation for Church of England).
'whit'+'esau'+'ce'='WHITE SAUCE'
(Other definitions for white sauce that I've seen before include "Food additive" , "Basic thick liquid appetiser" .)