Add water to a large saucepan to a depth of 1 inch; set a large vegetable steamer in pan. Bring water to a boil over high heat. Add broccoli florets to steamer. Steam broccoli, covered, 4 minutes or until crisp-tender. Place broccoli in a medium bowl. Add toasted sesame seeds, dark sesame oil, kosher salt, and freshly ground black pepper to broccoli; toss well.