Prepare the Chicken: Butterfly each chicken breast, then cut in half to create four thinner cutlets. Pat them dry with paper towels.
Set up a dredging station with three shallow dishes: In the first, whisk together flour, paprika, garlic powder, onion powder, salt, and pepper. In the second, whisk the egg and milk. In the third, place the panko breadcrumbs.
Dredge each chicken cutlet: first coat thoroughly in the seasoned flour, shaking off any excess. Then dip into the egg wash, allowing excess to drip off. Finally, press firmly into the panko breadcrumbs to ensure a thick, even coating.
Heat about 1 inch of vegetable oil in a large, heavy-bottomed skillet over medium-high heat to 350°F (175°C). Carefully add the breaded chicken cutlets, working in batches if necessary to avoid overcrowding the pan. Fry for 4-6 minutes per side, or until golden brown, crispy, and cooked through (internal temperature of 165°F). Remove the chicken to a wire rack set over a baking sheet to drain, and lightly season with salt.
In a small saucepan, gently warm the Buffalo sauce over low heat, or microwave until warm. Toss the crispy chicken cutlets in the warm Buffalo sauce until evenly coated.
Prepare the Ranch Slaw: In a medium bowl, whisk together mayonnaise, sour cream (or Greek yogurt), white vinegar, and sugar (if using). Add the shredded cabbage and crumbled blue cheese. Toss to combine. Stir in fresh chives and season with salt and pepper to taste.
Assemble the Sandwiches: Lightly toast the brioche buns. Place a buffalo chicken cutlet on the bottom half of each bun. Top with a generous scoop of the ranch slaw and pickle slices, if desired. Cover with the top bun and serve immediately.
Notes
The ranch slaw uses a blue cheese variation as specified in the recipe.