Pat chicken pieces dry with paper towels. In a shallow dish, combine flour, 1 tsp salt, 0.5 tsp black pepper, and paprika. Dredge each chicken piece thoroughly in the flour mixture, shaking off excess.

Heat vegetable oil in a large deep pan or Dutch oven to 350°F (175°C). Carefully add chicken pieces, ensuring not to overcrowd the pan. Fry for 8-10 minutes per side, or until golden brown and cooked through (internal temperature 165°F/74°C).

Remove fried chicken from the pan and place on a wire rack set over paper towels to drain excess oil. Set aside.

In a separate small pan, heat 1 tablespoon of the frying oil (or fresh oil). Add minced garlic and sliced red chilies. Fry over medium heat for 1-2 minutes until fragrant and garlic is lightly golden, being careful not to burn it.

Stir in fish sauce, brown sugar, rice vinegar, and water. Bring to a simmer. Cook for 2-3 minutes until the sugar is dissolved and the sauce slightly thickens.

Whisk in the cornstarch slurry and cook for another minute, stirring continuously, until the sauce thickens to your desired consistency.

Add the fried chicken pieces to the pan with the sauce. Toss gently to coat all the chicken evenly. Serve immediately, garnished with fresh cilantro if desired.