Offal soup's first, then we film sitcom (10)
I believe the answer is:
sweetbread
'offal' is the definition.
(I've seen this before)
'soup's first then we film sitcom' is the wordplay.
'soup's first' becomes 's' (1st letter of 'soup').
'then' says to put letters next to each other.
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
'sitcom' becomes 'bread' (BBC sitcom).
's'+'we'+'et'+'bread'='SWEETBREAD'
(Other definitions for sweetbread that I've seen before include "Thymus gland as food" , "Veal offal" , "Pancreas (as food)" .)