Coat crabs with flour seasoned with salt and pepper. Saute in 3 T. hot oil in large skillet over medium heat until golden brown on both sides, about 4 minutes. Cover and cook 1 minute. Remove from skillet and keep warm.
Wipe out skillet. Saute shallots in remaining 3 T. hot oil over medium-high heat 1 minute. Add ginger; saute 1 minute. Add broth and scallions; heat to boiling. Reduce heat and simmer 2 minutes.
Dissolve cornstarch in soy sauce and sherry. Stir cornstarch mixture into skillet. Boil, stirring constantly, until thickened.
Spoon sauce over crabs on serving platter and sprinkle with sesame seeds. Serve hot.