Combine buttermilk, tomato sauce, salt and pepper and chilli and mix well. Pour into a shallow dish and add chicken. Toss to coat. Cover and refrigerate for 30 minutes or overnight

In a separate bowl, combine flour, cornflour, garlic salt, white pepper and salt

Fill a large frying pan with enough oil to come 2cm up the side. Heat over medium-high heat until hot and oil is shimmering

Using tongs, remove one chicken thigh from marinade, allowing excess to drip off. Toss in flour mixture, making sure to coat both sides evenly. Cook in batches in hot oil for 4-5 minutes each side, or until coating is golden and crisp. Transfer to a tray lined with paper towel. Keep warm in a low oven

Add cabbages, carrot and green onion in a large bowl. Mix together mayonnaise and tomato sauce and toss through coleslaw

To serve, spoon extra mayonnaise onto the bottom of the hamburger bun. Drizzle over extra tomato sauce. Add crispy chicken and top with coleslaw. Cover with bun tops. Serve immediately with sweet potato fries