Inspired by a similar dish at Karasu in Brooklyn. You could also put the sauce on spinach (which is traditional) or any other dark green, corn, endive, fried or grilled eggplant, tofu, roasted carrots or squash, or broiled cabbage. The dish will keep for up to 4 days in the fridge. —Ali Slagle
Bring a pot of salted water to a boil. While you wait for the water to boil, trim the rabe and cut each piece in half. When the water is boiling, blanch the greens in the water for just under a minute. Drain and let cool.
Put the sesame seeds in a dry skillet over medium heat and heat until a few shades darker, 2 to 3 minutes. Transfer to a mortar and pestle or suribachi and let cool a bit. Grind the seeds until very coarse—you do not want to make a paste
In a mixing bowl, combine the soy sauce, mirin, sugar, and ground sesame seeds. Squeeze the rabe to make sure the majority of its moisture has drained off. Add the rabe to the dressing and stir to coat.