Place a rack in middle of oven; preheat to 425 Degrees F.
Whisk together egg yolk, 3 Tb./ mayonnaise, 1 Tb. mustard, 1 1/2 tsp., Kosher salt and black pepper in a large bowl until smooth
Pat chicken dry with paper towels. With your knife parallel to the cutting board, slice breast into 1/2 "- thick cutlets (smaller breasts need no cutting). Place in bowl and turn with tongs to evenly coat. Set aside
Heat oil in a medium skillet over medium. Add a pinch of panko. If tiny bubbles apper instantly, you"re good to go. Add remaining panko and cook, stirring, until golden bown, about 5 minutes. Let panko cool in pan about 5 minutes.
Set chicken next to panko and place a wire rack set inside a rimmed baking sheet nearby. Using tongs, place a piece of chicken in panko and pat all over with panko, pressing firmly to adhere.
Lightly shake off excess and place chicken on rack. Repeat with r3emaining chicken, spacing evenly apart on rack. Discard any remaining panko.
Bake chicken until cooked through and breadcrumbs are deep golden brown, 10-15 minutes. Let cool slightly.
Stir honey, cayenne, and remaining 1/4 cup mayonnaise and 1/4 cup Spicy Beer Mustard in a small bowl; season with lack pepper. Add chives or finely diced green onion tops to sauce.
Serve chicken with sauce alongside for dipping