Slice off the tough ends, and cut kailan in halves, lengthwise. Wash thoroughly in a few changes of water to remove soil particles and grit. (If using other varieties of kailan, please read Recipe Notes below). Drain off excess water and set aside.
In a small bowl, combine sauce ingredients and stir to mix well. In a separate bowl, combine corn flour and water.
Heat up a wok over medium heat. When wok is hot, reduce to low heat, add cooking oil.
When oil is hot, tip in the minced garlic and stir fry continuously until garlic just starts to turn a light golden brown.
Turn off the heat and remove garlic immediately with a slotted spoon (Note: Garlic burns quickly once it turns golden brown, and will taste bitter). Leave the garlic-infused oil in the wok.
Heat up the wok with garlic-infused oil over high heat.
When hot again, tip in the vegetables all at once and stir fry vigorously for 1 minute, or until stems and leaves just start to soften and turn limp.
Add the sauce, and thicken with corn starch solution to desired consistency. Remember to stir the cornstarch solution vigorously before adding in.
Dish out onto serving plate, garnish with fried garlic bits, and serve immediately.
Depending on the variety of kailan you are cooking, you may need to discard or peel the outer, tougher fibrous layer off the kailan stems using a short-bladed kitchen knife. This will also allow the kailan stems to cook through quickly, and minimise the risk of overcooking.
If you are cooking a long-stemmed variety where the stems are to be cooked as well, it is a good practice to separate the leaves from the stems. When ready to stir fry, fry the stems first until slightly softened, followed by the leaves.
Alternatively, after peeling the outer, tough fibrous layer, you may slice the stems thinly if stems are quite thick. This way, the stems and leaves can be tipped into the hot oil at the same time.
You can combine sauce ingredients and corn starch solution together in a bowl. However, it will be harder to control the consistency of the sauce. With experience, you can eyeball how much thickening solution is needed for the amount of sauce you prepare.