In a large pot of rapidly boiling salted water, blanch rapini, whole for 2 minutes.
Drain and plunge in ice cold water to stop cooking. Drain.
In a small bowl, whisk together rice vinegar, sesame oil and sugar
In a large saute pan or wok, heat oil over a medium high heat until smoking.
Add garlic, sesame oil and rapini and chopped cashews and stir fry for 1 minute. Next, add vinegar, sesame oil and sugar mixture stirring another 30 seconds.
Add salt and red pepper flakes to taste.