01 - Rinse the chicken thoroughly under cold water. Place in a large pot and cover with 12 cups cold water.
02 - Add the onion, garlic cloves, ginger, 2 whole green onions, and daikon radish (if using). Bring to a boil over medium-high heat, skimming off any foam that rises to the surface.
03 - Reduce heat to low, cover partially, and simmer for 1 hour until the chicken is cooked through and tender.
04 - Carefully remove the chicken and set aside to cool slightly. Strain the broth through a fine mesh sieve, discard solids, and return clear broth to the pot.
05 - Shred the chicken meat into bite-sized pieces, discarding skin and bones. Return shredded chicken to the broth. Season with 1–1½ tsp salt and black pepper, adjusting to taste.
06 - Simmer gently for another 10 minutes to allow flavors to meld together.
07 - In a small bowl, combine soy sauce, rice vinegar, sesame oil, sesame seeds, green onion, and chili flakes. Mix well.
08 - Serve hot soup in bowls, topped with sliced green onion. Offer dipping sauce on the side for dipping the chicken.