Place the boneless skinless chicken breasts in a large mixing bowl. Pound them gently with a meat mallet or rolling pin until about ½ inch thick for even cooking.
In another bowl, whisk together the buttermilk and egg until smooth. Pour this mixture over the chicken breasts, cover, and refrigerate for at least 1 hour or overnight.
In a shallow dish, mix together the all-purpose flour, cornstarch, kosher salt, garlic powder, ground black pepper, and white pepper to create the breading.
Remove the chicken from the buttermilk marinade, letting excess drip off. Dredge each piece in the flour mixture, coating evenly. Shake off excess flour and set aside.
Heat about ½ inch of vegetable oil in a large skillet or deep fryer over medium-high heat. Use a thermometer to ensure the oil reaches 350°F (175°C).
Carefully add the breaded chicken to the hot oil, frying in batches if needed. Cook for 5-7 minutes per side until golden brown and cooked through (internal temperature 165°F or 75°C).
Remove chicken from oil and place on paper towels to drain. Let rest while preparing the gravy.
In the same skillet, reduce heat to medium and melt the butter. Whisk in ½ cup flour, stirring for about 2 minutes until golden brown. Gradually whisk in 2 cups whole milk, simmer until thickened. Season with salt and pepper to taste.
Serve the crispy Chicken Fried Chicken hot, drizzled generously with creamy gravy. Enjoy with your favorite sides.