He pretends to be impartial, but believe me, he 'knows which side his bread is buttered on'.
I took the job because I needed to earn some 'bread'. [=(more commonly) 'dough']
Casual clothing has always been the company's 'bread and butter'.
(..) Why, l'll-- Your best friend? And what am l? Just your conscience. Okay, that settles it. - B-But,Jiminy-- - You buttered your bread, now sleep in it. Ha-ha-ha! Go on, laugh. Make a jackass out ofyourself. l'm through! This is the end. But,Jiminy, Lampwick says a guy only lives once. (..)1940 Pinocchio