1. Preheat Your Oven and Prepare the Dish: Start by preheating your oven to 375 F (190 C). Lightly grease an 8×8 inch or 9×9 inch baking dish with cooking spray. This prevents sticking and makes cleanup easier.

2. Combine the Wet Ingredients and Chicken: In a large mixing bowl, combine the shredded or diced cooked chicken, condensed cream of chicken soup, buffalo wing sauce, and milk. Stir everything together until the ingredients are well mixed and the chicken is evenly coated.

3. Add the Cheese (Most of It!): Stir in 3/4 cup of the shredded cheddar cheese and all of the crumbled blue cheese (if using) into the chicken mixture. Reserve the remaining 1/4 cup of cheddar cheese for the topping. Mix gently until the cheeses are distributed throughout the mixture.

4. Transfer to Baking Dish: Pour the entire chicken mixture into your prepared baking dish. Spread it out evenly with a spoon or spatula to ensure an even layer for baking.

5. Top with Remaining Cheese: Sprinkle the remaining 1/4 cup of shredded cheddar cheese evenly over the top of the casserole. This will create a lovely golden, bubbly crust.

6. Bake Until Bubbly and Golden: Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the casserole is hot and bubbly around the edges and the cheese on top is melted and lightly golden brown.

7. Garnish and Serve: Once baked, carefully remove the casserole from the oven. Let it rest for 5 minutes before serving. If desired, sprinkle with chopped green onions for a fresh pop of color and mild onion flavor.