1Pat chicken dry with paper towels. Toss chicken pieces with 0.5 cup cornstarch, salt, and black pepper until evenly coated.
2Heat 3 tbsp vegetable oil in a large skillet or wok over medium-high heat. When shimmering, working in batches if needed, cook chicken until golden and cooked through, about 8–10 minutes per batch. Transfer to a plate.
3In the same skillet, reduce heat to medium. Add garlic, ginger, and whole dried chilies. Toast for 30 seconds until fragrant.
4Whisk together soy sauce, rice vinegar, sugar, and chicken broth in a small bowl. In another bowl, mix 1 tbsp cornstarch with 1 tbsp water to make a slurry.
5Pour the soy mixture into the skillet. Bring to a simmer, then stir in the cornstarch slurry. Cook for 1–2 minutes until the sauce thickens and turns glossy.
6Return the chicken to the skillet and toss to coat completely in the sauce. Drizzle with sesame oil and scatter white parts of scallions over top. Cook for 1 minute more.
7Garnish with green scallion tops and serve immediately over rice.