Pound the chicken breasts to an even thickness. Combine the buttermilk, hot sauce (optional), and eggs in a bowl. Add the chicken breasts, ensuring they are fully submerged. Cover and refrigerate for at least 2 hours or overnight.
Mix the flour, baking powder, garlic powder, onion powder, cayenne pepper, kosher salt, and black pepper in a shallow dish. This will be the breading for the chicken.
Remove the chicken breasts from the buttermilk marinade, allowing any excess to drip off. Dredge the chicken in the flour mixture, pressing gently to adhere the breading to the chicken.
Preheat the air fryer to 390 degrees F, using the preheating butter, or preheat for 5-6 minutes. Carefully place the breaded chicken breasts into the preheated air fryer.
Air Fry for about 6-8 minutes per side or until the chicken is golden brown and cooked through. Ensure the internal temperature reaches 165°F (74°C).
Spread mayonnaise on both sides of the brioche buns. Place a fried chicken breast on the bottom bun. Top with pickle slices and cover with the top bun.
Your homemade Popeyes Chicken Sandwich is now ready to be enjoyed. Serve it while the chicken is still warm and crispy.