Karen Tran remembers the first time she saw pot stickers being demonstrated at a Costco store in California. Amid the bustling sample-fest at the warehouse-club outlet on a Saturday morning, shoppers were swarming to the lady who was microwaving and putting out Ling Ling Asian Kitchen pork and vegetable dumplings. They disappeared into consumers’ mouths as quickly as she could place them on a tray.
“Ling Ling had a great recipe and put out tons of samples and it just snowballed,” says T…