Cover the chicken with 6 cups water (more, if needed to fully cover the chicken) in a large pot. Add the onion, garlic, ginger, sesame oil, and soy sauce. Season liberally with salt. Bring to a boil over high heat. Reduce heat and simmer, uncovered, for at least 1 hour or until the chicken is falling off the bone and the broth has deepened in color and has reduced to no more than 3 cups.