Preheat air fryer to 375°. Grease six 6-oz. ramekins with 2 tablespoons butter. For topping, in a small bowl combine 2 tablespoons butter, peanuts, 3 tablespoons bacon and brown sugar; set aside., In a large bowl, beat muffin mix, buttermilk and eggs. Microwave peanut butter and remaining 2 tablespoons butter until melted; stir into batter. Fold in peanut butter chips and remaining 2/3 cup bacon. Pour into prepared ramekins; sprinkle with topping., Place ramekins on tray in air-fryer basket; cook until a toothpick inserted in center comes out clean, 10-15 minutes. Cool 5 minutes before removing from ramekins to a wire rack. Serve warm. If desired, drizzle with caramel ice cream topping.