Black-Sesame Salmon Balls

Spread the salmon cubes on a plate and freeze for 15 minutes. Transfer the salmon to a food processor. Add the water chestnuts, egg white, cornstarch, wasabi powder, three-fourths of the scallions, 1 1/2 teaspoons of the ginger, 2 teaspoons of kosher salt and a pinch of pepper. Pulse 4 or 5 times, until the salmon is chopped and the mixture just comes together. Transfer to a bowl.

Spread the sesame seeds on a plate. Scoop the salmon mixture into mounds of 2 tablespoons each and roll into 24 balls. Roll the balls in the seeds and transfer to 2 glass pie plates. Set one of the plates in a large steamer. Steam the salmon balls over boiling water until firm, about 6 minutes. Repeat with the remaining salmon balls.

Meanwhile, in a bowl, combine the vinegar, soy sauce and sesame oil with the remaining scallions and ginger. Serve the salmon balls with the dipping sauce.