Beef in black bean sauce

Name: Beef in black bean sauce
Ingredients: 300g/10½oz rib-eye or rump steak; 1 tsp sesame oil; 1 tsp sugar; 1 pinch Chinese five-spice powder; 1 tbsp light soy sauce; 1 tbsp cornflour; 1 tbsp oyster sauce; 1 tsp dark soy sauce; 2 tbsp rice wine; 1 ladleful chicken stock, water, beer or lager (about 5 tablespoons); 2 tsp salted fermented black soy beans; 2 garlic cloves, finely chopped; 3cm/1¼in fresh root ginger, peeled and finely chopped; ½ brown onion, sliced; ½ green or red pepper, sliced; 1 spring onion, roughly chopped, plus extra to garnish (optional); 3 cavolo nero or kale leaves, roughly chopped; 2 tbsp vegetable oil; chopped fresh coriander, to garnish (optional)