Combine all the marinade ingredients in a bowl and whisk until the sugar dissolves. Add the chicken pieces and toss to coat. Cover and refrigerate for 12 to 24 hours, turning once or twice.

Remove the chicken from the marinade and reserve the marinade.

Heat the oil in a large, heavy skillet (cast iron or stainless steel) over medium-high heat until shimmering. Add the chicken in a single layer without crowding the pan, working in batches if needed. Sear the chicken for 3 to 4 minutes per side until browned and cooked through to an internal temperature of 165°F.

While the chicken cooks, pour the reserved marinade into a small saucepan and bring to a boil. Lower the heat and simmer for 5 minutes. Whisk in the cornstarch slurry and continue stirring until the sauce turns glossy and thickens enough to coat a spoon, about 2 minutes more.

Remove the saucepan from the heat. Add the cold butter and swirl or whisk until fully incorporated and glossy. Do not return the sauce to the heat after adding the butter; it will break.

Pour the sauce over the cooked chicken in the skillet and toss to coat. Serve immediately over steamed white rice.