Mix the water, salt and vinegar in a large bowl. Place the chicken in the bowl and cover with cling film. Place in the fridge for at least a couple of hours or preferably overnight.
To make the slaw place all the ingredients in to a large bowl with a good sprinkling of salt and pepper. Cover and chill until ready to use.
To make the sriracha mayo place all the ingredients into a bowl and mix thoroughly. Cover and refrigerate until ready to use.
When you're ready to make your chicken remove it from the bowl and pat dry. Place the buttermilk in a bowl and the flour in a separate bowl. Add a tablespoon of pepper to the flour and stir in. Add three tablespoons of buttermilk to the flour and mix in with your fingertips so that clumps of the flour form.
Before you start frying the chicken, make the wedges. Preheat the oven to 180°Place the wedges on a baking tray with a good sprinkling of salt and pepper and the olive oil. Place in the oven for 30-40 minutes until cooked and crispy.
Now finish the chicken. Heat the oil in a saucepan and use a thermometer to make sure it gets to 425°F (it will go down in temperature when you add the chicken). Place the chicken thighs into the buttermilk. Take each piece of chicken out of the buttermilk and allow the excess to drip off. Place the pieces into the flour one at a time and make sure they're coated in a thick layer of flour.
Once the oil has reached the right temperature carefully place the chicken pieces into the oil. Make sure the oil stays between 300 and 350°Cook for about 2 minutes on the first side until it's really brown and crispy. Flip onto the other side and cook for another 2-3 minutes until the chicken is cooked through. Remove the chicken and place on a paper towel covered plate to soak up the excess oil. Sprinkle some salt over the chicken.
Remove the wedges from the oven and sprinkle with salt and the chopped thyme. Assemble the sandwiches by spreading some of the mayo on the bottom bun, top with a piece of chicken followed by some slaw, some more mayo and the top bun. Enjoy!