Preheat oven to 350°.
Drain your chiles, then cut them in half and remove the seeds.
27 oz can of whole hatch green chiles
Grease a 9x13 baking dish. Lay half the green chiles in a single layer on the bottom of the baking dish.
Cover the chiles with 1/2 of the cheese.
1 lbs grated cheese
Set aside one chile (to be used for decoration). Using the remaining chiles, place another layer of chiles over the cheese.
Cover the chiles with the rest of the cheese.
Separate the eggs. Whip the whites until stiff peaks form.
4 eggs
In a medium bowl, whisk together the yolks, milk, and flour.
2 cups milk, 2 Tbsp flour
Fold the stiffened egg whites into the milk mixture.
Spread the egg mixture evenly on top of the casserole.
Slide the remaining chile into thin strips. Press the strips down slightly into the egg mixture on top of the casserole.
Cover with foil and bake at 350° for 1 hour. Remove foil and bake for 10 more minutes to brown the top.
Allow casserole to cool for 15 minutes, then serve!