This classic soup can be found in many restaurants and almost every book of Cantonese specialities. This recipe comes from The Cook's Companion.
2 sweetcorn cobs, grated*
2 tbsp finely chopped spring onion
1 tsp freshly minced ginger
250g picked crab meat (2 medium blue swimmer crabs)
1 tbsp rice wine, or mirin or dry sherry
600ml chicken stock
2 tbsp light soy sauce
1 tbsp cornflour
2 tbsp water
2 tsp sesame oil
1 egg, whisked with a pinch of salt and
1 tsp vegetable oil
1 tbsp black or red Chinese vinegar
* To grate corn: I bought a gadget in the US for doing this. It is like a fork with curved prongs and you drag it through the kernels. It splits them and then the gadget is turned over, becoming a rake that tears the broken kernels and the milky juices from the cob. Alternatively, stand the cob on its end on a large, flat plate. Using a sharp knife and working down the cob, slice halfway through the kernels, then with the back of the knife, or a soup spoon, rake down the cob, "grating" the remainder of the kernels as you go, until you have extracted as much of the corn and milky juice as possible. The grated corn will look rather like scrambled eggs.
Grate corn from the cobs to make about 2 cups.
Heat 2 tbsp oil in a wok or heavy-based saucepan. Sear spring onion and ginger for 30 seconds.
Add crab meat, then sprinkle with salt and rice wine and stir lightly. Pour in corn, stock and soy sauce, stirring until soup comes to a boil. Reduce heat and simmer for 2 minutes.
Mix cornflour, water and sesame oil and stir until quite smooth, then add a little hot soup and stir to blend. Tip mixture back into soup, swirling it in evenly. Turn off heat and trail the egg mixture over surface, stirring slowly to break up strands.
Add vinegar and taste for salt. Adjust with soy sauce or serve soy sauce and additional vinegar alongside so guests can make their own adjustments.