Wrap ground black pepper in cheesecloth. Boil pepper in water for 10 minutes. Cool and discard water.
Remove large shells of crabs and discard fibrous tissue found under the shell. Divide each crab into 4 portions, breaking each body in half and separating large claws from body. Leave legs attach.
Heat oil in wok or large frying pan and fry crab pieces for 5 - 7 minutes to cooked crab. Add crushed garlic and roast until golden. Add Shaoxing wine, soy sauce, sugar, boiled black pepper, clams juice and bring to simmer. Mix cornstarch with enough cold water to make a paste and add to simmering stock.
Add green onions and serve with steamed jasmine rice on a hot platter and garnish with green onion pieces.