1. In a small skillet, toast the sesame seeds over moderate heat until fragrant, about 2 minutes. Transfer the sesame seeds to a plate to cool.
2. In a medium saucepan, bring the water to a boil. Add the broccoli florets and stems and cook until they are bright green, about 2 minutes. Using a slotted spoon, transfer the broccoli to a colander and refresh under cold water. Pat the broccoli dry with paper towels.
3. Add the sliced rib eye to the boiling water and cook until medium rare, about 40 seconds. Using a slotted spoon, transfer the beef to a plate. Spread the slices in an even layer and season them with salt and pepper.
4. In a large bowl, combine 3 tablespoons of the cooking water with the soy sauce, rice vinegar and sesame oil. Add the broccoli, sliced beef, kimchi and sesame seeds to the bowl and toss the salad well. Serve the beef and broccoli salad at once.