After seeing the signs in several nearby restaurants advertising Pork Bone Soup (Gam Ja Tang), I ask the kid behind the counter at Grandma's if they sell a version. He sneers that they don't serve that trendy stuff. But while it may be the hottest thing at Bloor and Palmerston these days, the dish has actually been around for millennia.So what is it? Think goulash goes to hell: thick cross-sections of pork shank slowly simmered in broth and thickened with potato, salty fermented toenjang miso paste and hellishly hot koch'u pepper powder. Popular throughout northern China and Japan as well as Korea, Pork Bone Soup is thought by its devotees to build immunity to disease, slow aging, promote growth in children and prevent freckles, acne and snoring.