In a large bowl, combine the buttermilk, dill pickle juice, egg, salt, pepper, garlic powder, and paprika. Add the chicken breasts, coating them well. Cover and refrigerate for at least 30 minutes (or overnight if time allows).

In another bowl, whisk together the flour, cornstarch, dried dill weed, baking powder, salt, and black pepper.

In a large skillet or deep fryer, heat the vegetable oil over medium-high heat until it reaches 350°F (175°C).

Remove the chicken from the marinade, allowing excess liquid to drip off. Dredge each breast in the flour mixture, pressing gently to ensure an even coating.

Carefully place the breaded chicken into the hot oil. Fry for about 5-7 minutes on each side or until golden brown and cooked through. Use a meat thermometer to ensure they reach an internal temperature of 165°F (74°C). Remove from the oil and let drain on paper towels.

While the chicken is cooling, mix the mayonnaise, chopped fresh dill, lemon juice, minced garlic, Dijon mustard, and season with salt and pepper to taste.

In another skillet, melt the butter over medium heat. Add the brioche buns, cut side down, and toast until golden brown.

Spread a generous amount of dill sauce on both sides of the toasted bun. Place a crispy chicken breast on the bottom bun, add a slice of cheddar cheese, top with shredded lettuce, and dill pickle chips. Cap it off with the top bun.