1In a small bowl, mix together soy sauce, hoisin sauce, rice vinegar, chilli paste, and sesame oil.
2Marinate the chicken with 2-3 tablespoons of the sauce mixture, grated ginger, and grated garlic. Mix well and let marinate for about 30 minutes.
3After marinating, add 2 cups of cornstarch to the chicken and toss to coat evenly. Shake off excess cornstarch and keep pieces separated.
4To the remaining sauce mixture, add brown sugar, 2 tablespoons cornstarch, and chicken stock. Mix well and set aside.
5Heat oil in a deep pan or wok over medium-high heat. Fry the chicken pieces in batches for about 3 minutes, turning halfway, until golden brown and crispy. Remove and drain on paper towels.
6In a separate skillet, heat oil or melt butter. Add chopped garlic and chopped ginger, sauté for 1 minute until fragrant.
7Add the prepared sauce to the skillet, bring to a simmer, and stir until it thickens.
8Add the fried chicken to the sauce and toss to coat evenly.
9Transfer to a serving plate, garnish with chopped green onion and sesame seeds. Serve immediately.