The Asian trinity of soy, ginger, and garlic is an excellent match for broccolette, which is a cross between broccoli and Chinese broccoli (gai lan). To maintain the broccolette's bright green color, it's blanched first, which partially cooks the broccolette and sets its bright emerald color. Then it's stir-fried with the aromatics and sauce until crisp-tender and piping hot. This recipe uses two kinds of sesame oil. Plain sesame oil is used to stir-fry the broccolette because it can tolerate high heat without burning. Toasted sesame oil has great flavor but doesn't stand up to high temperatures, so it's used in only the sauce. The cashews add a sweet crunch to this dish, but you could substitute almonds or leave out the nuts altogether if you prefer.
Bring a large pot of water to a boil and add 2 teaspoons of salt. Add the broccolette and cook for 4 minutes. Drain, then immediately plunge the broccolette into a bowl of ice water to stop the cooking process. When the broccolette is cool, drain thoroughly, and dry the spears with a clean kitchen towel or paper towels. Set aside.
Combine the rice vinegar, tamari, toasted sesame oil, and mirin in a small bowl and set aside.
Heat the plain sesame oil in a wok or large skillet over medium heat. Add the cashews and coriander; cook, stirring constantly, for 1 minute. Add the ginger, garlic, and broccolette to the wok and increase the heat to medium-high. Stir fry until the broccolette is hot, about 2 minutes. Add the vinegar-soy mixture and cook, stirring constantly, until the broccolette is crisp-tender and the sauce has glazed the vegetables.
Transfer the broccolette to a platter and sprinkle with the sesame seeds. Serve immediately.