2.) Chop up some onion (as much or as little as you like) and saute in 1/4 cup of butter just until translucent. They don't need to be charred. Then add 1/4 cup flour right on top of that and stir until thick and cohesive.
3.) Pour in 1 cup milk and stir until bubbling and thickened. Then add 1 cup salsa. Stir until hot (though you could say this mix is automatically hot since you just added spicy salsa!). Turn off (or down) the heat and salt to taste. Usually about 1/2 teaspoon is good.
4.) The chicken should be cool enough now so shred it into bit sized chunks and stir it into the sauce.
5.) Now begin to layer the casserole. Into your dish of choice (9x13, cast iron is really good) spread first a bit of sauce on the bottom. Put in a tortilla (if it doesn't fit then rip it into shape and use the pieces somewhere else in the casserole).
6.) Cover the tortilla with sauce and cover that with some cheese.
7.) Repeat until the sauce is gone. Go for about four layers. The top should be pretty liberally covered so nothing scorches as it cooks in the oven. And anything that drips down the side of the layers will get crispy and crunchy. My husband says it tastes like Cheez-Its.
8.) Bake in a 375 degree oven for about 30 minutes. If you're too hungry to wait, you can pull it out as soon as it's all bubbling and the cheese is beginning to brown on top.
The whole family LOVED this casserole! We will be making it often in the future!
I think I might add olives next time, too.
I add olives to everything, whenever possible.