01 - Heat oven to 350°F (180°C).
02 - In a large bowl, combine cream cheese, sour cream, ranch dressing, buffalo hot sauce, garlic powder, and black pepper; blend until smooth.
03 - Fold in shredded chicken, mozzarella, and blue cheese if using, mixing evenly.
04 - Transfer mixture to an 8x8 inch (20x20 cm) baking dish and spread uniformly.
05 - Bake for 20 to 25 minutes until the dip is hot and bubbly.
06 - Remove from oven and allow to rest for 5 minutes.
07 - Serve warm alongside fresh celery sticks.