You may find different varieties of baby bok choy at the market. We recommend using the short dark-green variety, sometimes called dwarf bok choy but often labeled simply “baby bok choy.” If you can only find Shanghai baby bok choy, which has bigger heads than the dark-green one, break the Shanghai variety into individual leaves rather than halving it. Thinly sliced lean beef rolls are a popular cut for hot pot and can found in the freezer aisle of Asian grocery stores.