https://www.saveur.com/article/Recipes/Asian-Greens-with-Garlic-Sauce/?con=asian-greens-with-garlic-sauce&dom=SAV&lnk=2&loc=recent
If you can't find choy sum for this Chinese recipe, whole baby bok choy or other leafy asian greens make a fine substitute.
garlic saucechoy sumasiangreensrecipe