1. Put the beef in a bowl,add the Shaoxing wine and salt and mix well.
2. Turn the tofu out onto a board and cut into cubes:3 slices down the length and 4 slices across. Be careful,as you don't want the cubes to break up. Place in a bowl that you can fit in a steamer.
3. Heat the oil in a wok over a high flame until slightly smoking,add the chilli,garlic and black beans and cook until fragrant. Add the beef and stir until fragrant,pour in the stock and soy sauce and bring to the boil.
4. Reduce the heat and simmer for 2 minutes. Add the potato flour mixture and stir as the liquid thickens. Add the shallot,then turn off the heat and stir in the sesame oil and chilli oil.
5. Meanwhile,steam the tofu over a pot of boiling water until hot,about 5 minutes.
6. Place the tofu into a large bowl,then spoon over the beef and sauce. Serve immediately.