To make the buttermilk brine, whisk all the ingredients together in a shallow bowl. Add the chicken thighs, cover with cling film and leave in the refrigerator for 12-24 hours.
The next day, to make the wet batter, whisk the egg and milk together in a bowl until combined. Set aside. For the flour coating, blend all the ingredients together in a medium bowl with a whisk.
Remove the chicken thighs from the brine and shake off the excess buttermilk. Lightly dip the thighs into the flour mix, then submerge them in the wet batter. Dredge them back into the flour and work in with your hands to give some texture almost like cornflakes.
Heat the oil for deep-frying in a deep-fryer or a large, deep saucepan to 140°C, or until a cube of bread dropped in sizzles in 40 seconds. Deep-fry the chicken in pairs for 7 minutes, then remove and set aside. Increase the temperature of the oil to 180°C, or until a cube of bread dropped in sizzles in 30 seconds. Deep-fry the chicken again for 3-4 minutes until golden brown and cooked through. Remove and drain on paper towels.
To build the sandwiches, cut the avocados in half and scoop the flesh out into a bowl. Add the lime juice, coriander, season with salt and pepper and mix together. Preheat the grill to medium. Grill the bacon to your liking. Cut the bread rolls in half and brush each half with
melted butter, then toast under the grill or face down in a hot dry frying pan for 2 minutes. Spread some of the avocado mix onto the base of each roll and top with a fried chicken thigh. Spoon over some of the hot sauce (be generous), top with a cheese slice and 2 slices of bacon each. Add some pickled onions on top. Spread a little of the mayonnaise on the lid of the bread roll and close the sandwich. It’s messy, but a killer sandwich.