Mix the Batter: In a mixing bowl, whisk together the flour, cornstarch, baking powder, salt, and black pepper. Gradually add cold water while stirring until the batter reaches a thick, smooth consistency.

Coat the Chicken: Add the chicken pieces to the batter and ensure they are evenly coated.

Fry the Chicken: Heat vegetable oil in a deep pan or skillet over medium-high heat. Fry the battered chicken pieces in batches until golden brown and crispy, about 3-4 minutes per side.

Prepare the Sauce Base: In a small saucepan, combine lemon juice, chicken broth, sugar, soy sauce, and lemon zest.

Enhance the Sauce: In a separate bowl, combine the cornstarch with water to create a smooth mixture. Slowly pour the mixture into the sauce while stirring constantly. Let it cook for 2-3 minutes until the sauce reaches your desired thickness. For a tangy twist, add a splash of rice vinegar if you like.

Coat the Chicken: Place the fried chicken in a large bowl. Pour the lemon sauce over the chicken and toss gently to coat each piece evenly.

Garnish and Enjoy: Transfer to a serving dish and garnish with sesame seeds and chopped green onions, if desired.