Crab Melt Sandwiches

Preheat broiler.
If using king crab legs, split them lengthwise and cut crosswise into 4-inch lengths.
Arrange legs, shell sides down, on a steamer rack set over a kettle of simmering water and steam, covered, 7 to 10 minutes, or until heated through.
Remove rack from heat and let crab stand, covered, until just cool enough to handle.
Working over a bowl, with a fork extract crab meat from shells, discarding cartilage and allowing juices to accumulate in bowl.
Using your fingers, separate crab meat into large shreds.
(If using lump crab meat, put in a bowl but do not shred.)
Add 1 tablespoon lime juice and toss to combine.
In a small bowl whisk together remaining tablespoon lime juice, mayonnaise, and mustard until smooth.
Pour sauce over crab and toss to coat.
Season crab mixture with salt and pepper and chill, covered, 30 minutes.
Lightly toast brioche or challah and with a 3 1/4-inch round cutter cut out rounds.
Lightly butter toast.
Spoon one fourth crab mixture into a 1/2-cup measure.
Holding a toast round on top of mixture in measure, invert crab onto round and set on an ungreased baking sheet.
Repeat procedure with remaining crab mixture and rounds and sprinkle 1 tablespoon Parmesan over each sandwich.
Broil sandwiches about 3 inches from heat until cheese is melted and golden, 1 to 2 minutes.
Serve sandwiches with lime wedges and garnish with chives.