1. First, clean the bok choy: remove all the leaves from the core and discard the center portion. Clean and rinse the leaves (leave them whole), drain them, and pat them dry.
2. Combine oil, ginger, and scallions in a large wok or cast iron skillet. Heat the wok over medium-high heat (yes, after you’ve added the foods—this keeps the delicate ginger from burning) and cook for 2-3 minutes until the pan is warm and the oil is beginning to sizzle and get fragrant.
3. Add the bok choy and toss with the oil. Cook for 2-3 minutes, stirring frequently, until the bok choy begins to soften and brighten.
4. Add the sesame oil, soy sauce, and sake. Cook uncovered for another minute or two, stirring frequently, until the sauce is bubbling and coating the bok choy.
5. Transfer to a serving dish, garnish with sesame seeds if desired, and serve.