Wash and pat dry the broccolini, trim the stalk and set it aside.
Whisk together vegetable stock and tapioca flour together and set aside.
Heat a wok on high heat.
Add the sesame oil, followed by the broccolini.
Saute it well for a minute and add the soy, the vinegar, sugar and toss it in well.
Add the vegetable stock that you kept aside earlier.
Toss it well. Saute it well and allow the sauce to thicken a bit.
Once the sauce looks sticky, remove from heat. Sprinkle the sesame seeds and get it ready to serve up.
Serve hot on a bed of steamed rice.