Kill live crabs, wash thoroughly and cut into pieces. Drain dry.
Heat wok over medium fire, add butter and let it melt. Add ginger and saute till fragrant.
Add crabs to wok and stir fry for a while till partially cooked, for about 3-4 minutes. (or simply skip this step if desired)
Remove crabs from wok and set aside. Add chicken stock, evaporated milk, shaoxing wine, salt & pepper, and bring the liquid to a boil.
Add crabs back into wok and cover wok with lid to allow crabs to cook for about 6-7 minutes. (The rule of the thumb is to cook crabs for 7-8 minutes per pound (0.45kg). If you have 2 crabs, take the average weight of the crabs rather than the total weight.)
While crabs are boiling, cook white beehoon and drain dry. Set aside.
Once crabs are almost done, add baby bok choy into wok and boil till cooked. Add white beehoon into wok after.