In a large bowl, mix soy sauce, sugar, garlic, and ginger. Add chicken, ensuring it's well coated. Marinate for at least 1 hour or overnight in the fridge.
In a large pot, place the marinated chicken and marinade. Add 2 cups of water, or enough to just cover the chicken.
Bring to a boil, then reduce heat to low. Simmer, covered, for about 30 minutes, turning the chicken halfway through.
Remove the lid, increase the heat to reduce the sauce until it thickens slightly, about 10 minutes.
Serve the chicken with steamed rice, garnished with scallions and sesame seeds if desired.
Notes
Marinate the chicken for at least an hour, or overnight for deeper flavor.
• Use a mix of light and dark soy sauce for the best flavor balance.
• Brown the chicken before simmering to lock in flavors.
• Keep the heat low and slow for the most tender chicken.
• Let the chicken rest in the sauce after cooking to absorb more flavors.