big potato, n.² — Green’s Dictionary of Slang

big potato n.²

[on model of Big Apple n.; Big Orange n.; potatoes are the main constituent of vodka]

(US) Moscow.

1988		Prime News 7 Jun. [CNN-TV] It’s summer in the Big Potato, as Moscow is affectionately known by its foreign residents [HDAS].
1992		News Hour 10 Jun. [CNN-TV] It might be a little early to expect sex shops on every corner here in the Big Potato [HDAS].