1) Grease or spray cooking spray on a 9 X 13 X 2 pan.
2) Place a layer of chiles, top with cheese & onion.
3) Continue building layers 2 or 3 more times.
4) Combine milk, eggs, baking powder, flour, salt & pepper.
5) Pour over chile/cheese layers.
6) Bake at 350 degrees 45-55 minutes, or until done.
7) Casserole is done when knife inserted in center comes out cleanly.
8) Serve with salsa, hot sauce or guacamole.