Method

• In a medium bowl, whisk together the soy sauce, mirin, brown sugar, 1/4 cup (60 ml) water, rice vinegar, sesame oil, garlic, and ginger until the sugar is mostly dissolved.
• In a small bowl, whisk together the cornstarch and 2 tablespoons (30 ml) cold water until completely smooth. Set aside.
• Pat the chicken thighs dry with paper towels: Cut them into evenly sized 1 1/2-inch (4 cm) pieces and season with the black pepper.
• Heat the neutral oil in a 12-inch skillet over medium-high heat until shimmering.
• Add the chicken in a single layer: If necessary, work in two batches to avoid crowding the pan. Cook undisturbed for 3 to 4 minutes, until the bottoms are deeply golden.
• Turn the chicken pieces and cook for another 3 to 4 minutes, stirring occasionally. They should be browned on several sides and nearly cooked through.
• Reduce the heat to medium: Pour the prepared sauce into the skillet and stir to coat the chicken. Bring to a gentle simmer.
• Simmer for 2 to 3 minutes, stirring occasionally, until the thickest chicken pieces reach 165°F (74°C).
• Stir the cornstarch slurry again, then slowly pour it into the skillet while stirring continuously.
• Simmer for 1 to 2 minutes. The sauce should become shiny and thick enough to coat the chicken without looking pasty.
• If the sauce becomes too thick, stir in 1 tablespoon (15 ml) water at a time. If it remains too thin, simmer for another 30 to 60 seconds.
• Toss the chicken through the sauce until every piece is evenly glazed and there is no pool of thin liquid at the bottom of the skillet.
• Remove the skillet from the heat and let the chicken stand for 5 minutes. The glaze will thicken slightly as it cools.
• Sprinkle with sliced green onions and toasted sesame seeds, if using. Serve warm.