In a medium bowl, combine soy sauce, brown sugar, salt, and pepper. Stir until the sugar dissolves, then add chicken thighs, ensuring they are fully coated. Marinate for 10 minutes while preparing the other ingredients.

Rinse 1 cup of jasmine rice under cool water until the water runs clear to remove excess starch. In a pot, bring 2 cups of salted water to a boil, then add the rinsed rice. Cover and cook for about 15 minutes on low heat until the water is absorbed.

Heat 2 tablespoons of vegetable oil in a large skillet over medium-high heat. Carefully place the marinated chicken thighs in the skillet, searing them for 5-7 minutes on each side until golden brown and cooked through, reaching an internal temperature of 165°F.

In the same skillet, add sliced onions, minced garlic, and grated ginger. Sauté for 2-3 minutes until the onions become translucent and fragrant.

Pour in 4 cups of chicken broth and 2 tablespoons of rice vinegar into the skillet, scraping up any browned bits from the bottom. Return the seared chicken to the skillet, bring to a simmer, and cook for an additional 5 minutes.

If you desire a thicker broth, mix 1 tablespoon of cornstarch with 2 tablespoons of cold water until smooth. Stir this into the simmering broth and let it thicken for another 2 minutes.

Spoon fluffy jasmine rice into bowls, then ladle the broth and tender chicken over the rice. Garnish with scallions and sesame seeds.