Green’s Dictionary of Slang

1. a baked potato, as sold in the street.

1837		‘Love in the City’ in Bentley’s Misc. June 589: Yellow cab upsets a pieman, and green demolishes an establishment of ‘all hot’.
1857		‘Ducange Anglicus’ Vulgar Tongue.

2. a seller of baked or chipped potatoes.

1837		‘Love in the City’ in Bentley’s Misc. Aug. 133: Pay the pieman, and mend young ‘All-hot’s’ tins.
1912		Western Times 2 July 5/3: The ‘All Hot’ Man. A Street Vendor pleaded not guilty to obstructing Wellington-street with a chipped potato cart.