Use a sharp knife to cut the kernels from the corn cobs. Place both the kernels and the cobs in a saucepan with the stock and simmer for 12 minutes. Discard the cobs. Scoop out half the kernels and set aside. Purée the remainder with a stick blender until creamy.
Return the whole kernels to the pan along with the Shaoxing wine, soy sauce and ginger. Mix the cornflour with the measurement water and stir into the soup along with the crabmeat. Simmer until heated through and slightly thickened. Season to taste.
Stirring the soup with a large spoon, slowly pour in the egg in one long stream to create silky strands of egg through the soup. Scatter over the spring onions and serve.