Preheat the oven to 350 degrees. Prepare a 9x13 baking dish with nonstick cooking spray.
Pour the chiles into the baking dish and create an even layer.
In a large mixing bowl, mix together the cream cheese, eggs, heavy cream, and seasonings until the eggs and cream cheese are well blended. Stir in the ground beef and 4 cups of the fiesta blend cheese.
Dollop the ground beef mixture over the top of the chiles to create a layer.
Top the casserole with the remaining cheese.
Bake for 30 to 35 minutes or until the eggs are completely set in the middle.
Allow the casserole to rest for 5 minutes before slicing and serving.
Serve with sour cream if desired.