Pick out chilis without cracks or flaws. I like to get them all about the same size. I grab extra because some tend to rip and its difficult to use. This is the tomato sauce i get, you can pick your heat.
Blister and char the peppers. I do this outside (it can leave your house smelling of burnt chilis) can be done under the broiler as well.
When chard, place into a tightly sealed container or a plastic bag, twist to keep the steam inside. Let sit for approx 30 minutes.
Skin the peppers, this can get pretty messy.
Cut a small slit into chile. Slip the cheese through the slit gently.
Lightly dust with flour. tap off excess
Beat the egg whites until stiff. it actually depends on how 'eggy' you like your peppers. add about 3 Tbs. of flour about 1/2 way thru beating the whites. then fold in the yolks, one at a time. again, depends on your liking. i use about 1/2 of the yolks.
Gently cover the pepper with the egg mixture and set into a pan with hot oil, med to med high heat. cook until slightly browned.
Layer the peppers into a pan as they are done browning. pour the el pato sauce over the top
Bake in 350 oven for approx 25-30 minutes
Before eating, sprinkle the cotija cheese over and then enjoy one of the best rellanos you have prob have ever had :-). some things just taste so much better if you put some time into it!