Make the croquettes: prepare a potato mash. Cook the onion and mince (season with the beef-style bouillon and mustard powder), then fold into the mash along with the finely diced carrot. Mix well with your hands and shape into little patties. (It's worth making a big batch – they freeze well.)
Set up a dredging station: coat each patty in the dry dredge (flour, salt, white pepper), then the wet mix (plant milk, dijon, flour), then the panko breadcrumbs.
Fry the croquettes until nicely golden and crispy; drain.
Make the curry dip: dissolve the Japanese curry roux cubes and cocoa powder into the water and simmer to a dippable sauce.
Make the tonkatsu sauce: stir together the Worcestershire, vegan oyster sauce, ketchup, mirin, and dijon.
Steam the bao. Assemble: spread on tonkatsu sauce, add a croquette and shredded cabbage, and fold. Serve with the warm curry sauce for dipping.
Plant-based. Method transcribed from the video (rough). From Liz Miu on Instagram.