Preheat the oven to 350°F. Spray a 12-inch round or oblong baking dish with cooking spray. Set aside.
In a heavy bottomed saucepan, melt together the half & half and cubed white American cheese. Cook over medium heat until the cheese is completely melted then add the cream cheese. Continue to cook stirring until fully combined. Add the fire roasted green chiles, garlic salt and onion powder. Mix well then remove from the heat.
Mix the thawed hash browns with the sauce.
Pour into the baking dish. Top with the remaining shredded cheese. Dot the top with cubed butter.
Bake 45 minutes until the potatoes are fork tender and the top is golden. .
Rest for 10 minutes then serve.