Brown ground beef and chopped onion. Add seasonings and flour and mix well.
Drain chilies and layer in the bottom a prepared casserole dish. Sprinkle with 3 cups cheese, then top evenly with meat mixture. Beat eggs, add milk, and pour over meat mixture.
Bake at 375°F for 45 minutes (check the last few minutes to be sure it isn't getting too brown. Serve with remaining shredded cheese and green onions for garnish.
Notes
Inspired by Chili Relleno Casserole from the Green Cattle BlogIf you prefer a more authentic cheese and it is available, you could substitute Queso Asadero.Use cooked beef and onions from the freezer to decrease your prep time.Substitute vegetarian ground crumbles to make a vegetarian version. I have made this with Beyond Beef Plant-Based Ground, which I prefer for the texture and taste.