Rinse rice in a strainer until water runs clear. Shake rice dry in strainer. Stir together rice, salt, and 1 1/3 cups cold water in a 1-quart Chinese clay pot. Let stand at room temperature 1 hour.
Heat rice mixture, uncovered and undisturbed, on a gas stovetop over medium-high until water along edges of clay pot begins to simmer in spots, 8 to 10 minutes. Continue simmering, uncovered and undisturbed, over medium-high until water is completely absorbed and rice makes a faint crackling sound, 5 to 6 minutes. Drizzle sesame oil evenly around inside edges of pot. Reduce heat to low; cover and cook until rice is just tender, about 10 minutes.
Working quickly, turn off heat, uncover, and arrange salmon belly, baby bok choy, and corn in an even layer on top of rice. Increase heat to medium-high. Cook, covered, until rice smells nutty and makes a constant crackling sound, 4 to 5 minutes. Turn off heat, and let stand, covered, on unlit burner 15 minutes. Slice green parts of scallions to equal 3 tablespoons, and sprinkle over salmon, baby bok choy, and corn. (Reserve remaining scallion for another use.) Serve with ginger-scallion sauce and mirin-soy sauce.
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