Brine the Chicken: In a medium bowl, whisk together the buttermilk, pickle juice, and 1 tsp of salt. Add the chicken thighs, ensuring they are fully submerged. Cover the bowl and refrigerate for at least 4 hours, or preferably overnight for the most tender results.

Prepare the Dredge: In a separate shallow dish or large bowl, combine the plain flour, cornflour, smoked paprika, garlic powder, onion powder, black pepper, remaining salt, and cayenne pepper. Whisk until everything is evenly distributed.

Set Up Your Station: Remove the chicken from the fridge about 20 minutes before you plan to fry. Place the bowl of brined chicken, the dish of seasoned flour, and a clean plate or wire rack next to your hob. This makes the dredging process much tidier.

Dredge the Chicken: Take one chicken thigh from the buttermilk, letting any excess drip off. Place it in the seasoned flour and toss to coat completely. Now, dip it *back* into the buttermilk for a second, and then return it to the flour for a final, generous coating. I find that pressing the flour firmly into the chicken on this second dredge is the real secret to those craggy, ultra-crispy bits we all love. Place the coated chicken on your clean plate and repeat with the remaining thighs.

Heat the Oil: Pour the oil into a large, heavy-bottomed pan or Dutch oven until it's about 4-5 cm deep. Heat over a medium-high heat until it reaches 175°C (350°F) on a cooking thermometer. Getting the temperature right is crucial for a non-greasy finish. For guidance on cooking chicken safely, the Food Standards Agency has helpful advice.

Fry the Chicken: Carefully place two chicken thighs into the hot oil, making sure not to overcrowd the pan. Fry for 4-6 minutes on each side, until deep golden brown and the internal temperature reaches 75°C (165°F).

Rest the Chicken: Once cooked, remove the chicken from the oil using tongs and place it on a wire rack to drain. This allows air to circulate, keeping the underside crispy. Let it rest for a few minutes while you fry the remaining chicken.

Prepare the Buns and Sauce: While the chicken is resting, split your brioche buns and lightly butter the cut sides. Toast them in a dry pan until golden. In a small bowl, mix the mayonnaise with the sriracha, if using.

Assemble Your Sandwich: Spread the spicy mayo on both halves of the toasted buns. Place a piece of crispy chicken on the bottom bun, top with sliced pickles and a generous handful of shredded lettuce, and finish with the top bun. Serve immediately.