Cut about a dozen tomatillos into 1 inch pieces. Cut up 2 cubanelle peppers about the same. Start this stuff sauteing in a bit of oil. When sizzling nicely, reduce heat to very, very low, cover and simmer for 30 minutes.You don't need to add any broth to this; the veg will render a lot of water. Let it cool a bit and then puree it in your food processor.
In another saute pan cook two 8 inch pieces of Mexican chorizo. Puree it. Add it to the sauce. The sauce now turns somewhat reddish due to the annato in the meat. I added some salt, some pepper, some ground guajillo chiles, some garlic.
Don't feel you have to make homemade ricotta from buttermilk just because I did (nyuck, nyuck). Layer corn tortillas (sliced up a bit to cover the size of the casserole) with sauce, ricotta and asadero cheese. I think it took 4 layers for mine.
Bake at 350 covered with foil for 30 minutes. Remove foil and bake another 15. Let rest for 5 or 10 and then plunge in.