Season the chicken: Pat the chicken thighs dry, then season both sides with salt, white pepper, and sesame oil. Let them rest for about 10 minutes.
Rinse the rice: Rinse the jasmine rice several times until the water becomes clearer. Drain it thoroughly.
Cook the aromatics: Heat the neutral oil in a heavy-bottomed pot over medium heat. Add the scallions, ginger, and garlic and cook until fragrant without browning the garlic.
Reserve some aromatics: Transfer about one-third of the cooked ginger, garlic, and scallion mixture to a small bowl for the sauce.
Toast the rice: Add the drained jasmine rice to the pot and stir for about 30 seconds, coating the grains with the aromatic oil.
Add the liquid: Pour in the chicken stock or water and add the salt. Bring the liquid to a gentle simmer.
Add the Hainanese chicken thighs: Arrange the seasoned chicken thighs over the rice in a single layer without overlapping them.
Cook gently: Cover the pot tightly, reduce the heat to low, and cook for about 20–25 minutes. Avoid repeatedly lifting the lid.
Check the chicken: Make sure the thickest part of the chicken reaches 165°F (74°C) before serving.
Rest the rice and chicken: Turn off the heat and keep the pot covered for 10 minutes so the rice can finish steaming and the chicken can rest.
Make the sauce: Combine the reserved aromatics with soy sauce, lime juice, sesame oil, fresh ginger, and optional chili.
Slice the chicken: Transfer the cooked chicken to a cutting board, rest briefly, then slice into strips or bite-sized pieces.
Fluff the rice: Gently fluff the fragrant rice with a fork or rice paddle.
Serve: Plate the rice with sliced Hainanese chicken thighs, cucumber, scallions, lime wedges, and the soy-ginger sauce.