Fill a heavy-bottomed pot with the water and place over medium heat. Drop in the smashed garlic, coriander root, lemongrass pieces, and galangal slices. Cover the pot and bring everything to a rolling boil — this will take about 10 minutes and helps extract maximum flavor from the aromatics.
Once boiling, add the fish sauce, light soy sauce, dark soy sauce, white pepper, and palm sugar to the pot. Stir everything together until the sugar completely dissolves, about 30 seconds. The broth should taste balanced — salty, slightly sweet, with a gentle heat from the white pepper.
Carefully nestle the chicken thighs into the simmering broth in a single layer. They should be about half-submerged — don't worry if they're not completely covered. Cover the pot with a lid to trap the steam and maintain gentle heat circulation.
Lower the heat to maintain a very gentle simmer — you want just a few lazy bubbles breaking the surface. Cook for 45 minutes total, flipping the thighs once at the halfway point so both sides absorb the flavors evenly. The chicken is done when it easily pulls away from the bone and the juices run clear.
⏱ 45 min
Remove the pot from heat and let the chicken rest in the warm broth for several minutes — this final resting keeps the meat juicy. Serve the chicken with jasmine rice and ladle some of the fragrant cooking broth over everything.