Part 1: Preparing the Creamy Chicken Base

1. Preheat and Prepare: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish (or a similar 2.5-3 quart casserole dish).

2. Combine the Sauce Ingredients: In a large mixing bowl, add the softened cream cheese, sour cream, and heavy cream (if using). Use a hand mixer or a sturdy whisk to beat the ingredients together until the mixture is smooth and there are no lumps of cream cheese.

3. Add Aromatics and Spices: To the same bowl, add the diced green chiles (with their juice), the chopped onion, minced garlic, ground cumin, chili powder, salt, and pepper. Stir until everything is well combined.

4. Fold in the Chicken and Cheese: Add the 4 cups of shredded chicken and 1 ½ cups of the shredded Monterey Jack cheese to the bowl. Use a spatula to gently fold everything together until the chicken is evenly coated in the creamy sauce.

Part 2: Assembling and Baking the Casserole

1. Transfer to Baking Dish: Spread the chicken mixture evenly into the prepared baking dish.

2. Top with Remaining Cheese: Sprinkle the remaining 1 cup of shredded Monterey Jack cheese evenly over the top of the casserole.

3. Bake to Golden Perfection: Place the casserole in the preheated oven and bake for 25-30 minutes. The casserole is done when the edges are bubbly and the cheese on top is melted and turning golden brown in spots.

4. Rest Before Serving: This is a crucial step! Let the casserole rest for at least 10 minutes after removing it from the oven. This allows it to set up, making it easier to serve and preventing it from being too runny. Garnish with fresh cilantro or sliced green onions if desired.