Green’s Dictionary of Slang

a cheap beefsteak.

1857		‘Ducange Anglicus’ Vulgar Tongue 2: Ben-Flake, n. A steak, used at a slap-bang, i.e. a low cook-shop or eating house.
1859		Hotten Dict. of Modern Sl. etc.
1859		Matsell Vocabulum.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.