Cook corn in a 1-quart saucepan of boiling salted wateruntil very tender, 3 to 5 minutes, and drain in a sieve.
Purée milk and hot corn in a blender until almost smooth, then force through a very fine sieve into a bowl, discarding solids.
Whisk in egg and salt and divide custard among ramekins.
Steam custards in a steamer set 1 inch above simmering water, covered with lid, until centers are set and a thin knife inserted into center of 1 custard comes out clean, 6 to 8 minutes.
Remove ramekins from steamer with tongs and cool custards slightly.
Coarsely chop 1/4 cup crabmeat and reserve remainder for another use.
Heat butter in a small heavy skillet over moderate heat until foam subsides, then cook crab, stirring constantly, until heated through, about 2 minutes. Stir in chives.
Serve custards topped with crab.
· Custard mixture can be prepared and poured into ramekins 1 day ahead and chilled, surfaces covered with plastic wrap. Bring to room temperature before steaming.
