In a large bowl, combine buttermilk, dill pickle juice, egg, salt, and pepper. Add the chicken breasts and ensure they are fully submerged in the marinade. Cover with plastic wrap and let it marinate in the refrigerator for at least 2 hours, ideally overnight.

In a shallow dish, mix all-purpose flour, cornstarch, dried dill, baking powder, salt, and pepper until well combined.

Once marinated, remove the chicken breasts from the buttermilk mixture, letting any excess drip off. Press each breast firmly into the flour mixture, ensuring an even coating. Dip the coated chicken back into the buttermilk for a second time, then re-coat it in the flour mixture.

In a heavy-bottomed pot or deep skillet, pour in vegetable oil and heat it over medium-high heat until it reaches 350°F (175°C).

Carefully place the coated chicken breasts into the hot oil, frying each piece for about 6-8 minutes on one side until golden brown. Then, flip and cook for an additional 6-8 minutes until the chicken reaches an internal temperature of 165°F (74°C).

While frying, prepare the creamy dill aioli by whisking together mayonnaise, chopped fresh dill, lemon juice, minced garlic, and a pinch of salt in a mixing bowl.

In a skillet over medium heat, melt some butter and toast the brioche buns cut-side down for 1-2 minutes until golden.

Spread a generous layer of the chilled dill aioli on the bottom half of each toasted bun. Add lettuce, the fried chicken, a slice of melted cheddar cheese, and dill pickles, then top with the other half of the bun.

Enjoy your Crispy Dill Chicken Sandwich hot for the best texture and flavor.