Season the chicken thighs generously with kosher salt. Make sure to coat all sides for maximum flavor. This step is crucial for enhancing the taste of the chicken.
In a 12-inch cast iron skillet, heat vegetable oil over medium-high heat until it shimmers. Carefully place the chicken in the skillet, skin-side down. Cook for about 5 to 6 minutes, or until the skin is a deep golden-brown color. Turn the chicken to cook the other side, and continue until both sides are beautifully browned.
Once the chicken is browned, remove it from the skillet and place it in a clean bowl. Set it aside as you prepare the sauce.
In the same skillet, add the garlic and sauté for about 2 minutes, allowing it to turn golden brown. This will infuse the oil with a lovely garlic flavor.
After the garlic is done, add the water to the skillet. Make sure to scrape up any browned bits from the bottom of the pan. These bits are packed with flavor and will enhance your sauce.
Stir in the brown sugar and allow it to cook for 3 to 4 minutes. You'll notice the sauce starting to thicken and darken in color. This is where the magic happens!
Add the rice vinegar and stir continuously as the mixture bubbles. Next, add the ginger, chicken broth, soy sauce, and if you’re using it, the fish sauce. Bring the mixture to a gentle simmer.
Carefully add the previously cooked chicken back into the skillet, placing it skin-side up. Let the chicken simmer in the sauce for about 20 to 25 minutes, or until it’s thoroughly cooked. You'll know it's done when the juices run clear.
Once the chicken is cooked, remove it from the skillet and place it on a plate. Let the sauce simmer for an additional 8 to 10 minutes until it thickens and coats the back of a spoon.
Return the chicken to the skillet and gently toss it to coat in the glossy sauce. Garnish with scallions and jalapeño pepper slices before serving.
