Buttermilk fried chicken

Name: Buttermilk fried chicken
Prep time: 30 min
Cook time: 40 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 10 chicken pieces (about 1¼kg/2lb 12oz), on the bone, skin on (use a mixture of thighs and drumsticks); 300ml buttermilk (see tips to make your own); 1 large egg; 1-2 litres groundnut oil; grilled corn on the cob, to serve (optional); skinny fries, to serve (optional); coleslaw, to serve (optional); zest 2 lemons; 1 tsp chopped thyme; 1 tsp paprika; 1 tsp onion salt; 1 tsp garlic granules; 1 tsp flaky sea salt; 225g plain flour; 2 ½ tbsp cornflour; 2 ¼ tsp garlic granules; 2 ¼ tsp salt; 2 ¼ tsp chilli powder