Wash and dry the poblano peppers. Decide how you like to roast the poblano peppers. See Notes For Roasting Methods
Once you have roasted the peppers, you can place them in a covered container, a plastic bag or even a paper bag to sweat the peppers. Most times I just cover them with a clean kitchen towel. let them sweat for 15-20 minutes.
When ready, carefully remove as much of the blistered skins away as possible from the poblanos. If the peppers overcook, they can be very soft and tend to tear. Be aware when handling them.
In my most recent video of me preparing chiles rellenos, I rinsed one of the poblanos under cool water to help me remove the small pieces of the blistered skins that remained. Many people commented that I should never do that! Lol! I wanted to try it because I saw a well known chef who is famous for cooking authentic Mexican food do it. I won't mention any names. In all honesty, I did not think it took any flavor away from the chile relleno in the end. Do whatever works for you.
Using a small sharp knife, slice a T at the base of the pepper, about 3/4 of an inch below the stem. Using a spoon or your fingers, carefully remove as much of the seeds as possible. If you have gloves, you can wear gloves to remove the seeds. Be careful not to pull on the loose membranes inside the pepper because it can cause the pepper to tear open.
Shredded cheese or a stick of cheese? I have used both. I decided that the shredded cheese could fill all the spaces in the poblano better than a stick of cheese. Again, do what works best for you. After stuffing all the peppers carefully, make sure they can still close all the way. Don't worry if they have some other tears besides where you initially sliced them. Just try to cover all the exposed spots with the pepper.
To freeze or not to freeze! A few years back I watched a video of a restaurant preparing huge quantities of rellenos. They shared how they would freeze the stuffed peppers for 1 hour to firm them up. This made is easier to dip the peppers in the batter. If you don't want to freeze them, that's ok. It makes it easier for me so that's why I do it. If freezing, place stuffed peppers on a plate lined with wax or parchment paper. Freeze for 35 minutes. In all the times I have used the freezing step, I have never had any issues with cold or frozen rellenos after I fried them. If you are not serving them directly after frying them, of course they will get cold as it sits.
When ready, remove the peppers from the freezer. Let them sit for a few minutes while you preheat the oil in a large skillet at medium heat. I try to let the oil preheat for a few minutes before I prepare the batter. In a large bowl, whip the egg whites for a few minutes until stiff peaks form. You should be able to turn the bowl upside down and the egg batter should stay in place. To the bowl, add 1 tsp. of salt, 1 tbsp. of flour and the egg yolks. Mix on low until smooth.
When you know the oil is hot enough (375 degrees F), then quickly unstick the pepper from the lined plate and dust with flour. Gently pat off excess flour. If the peppers are firm enough, holding the pepper by the stem, dip it into the egg batter and roll from side to side slowly to coat evenly with batter. You can use a small spoon to help you cover the pepper with batter. If the stem wants to tear away, you will use a large cooking spoon to place the relleno in the batter. There no way to sugar coat this! Lol! It can get messy and you have to multi tasks during these steps.
Carefully place relleno into hot oil. Let it cook for 30 seconds. Using a small spoon, gently spoon some hot oil over the egg batter. If you do this too fast, it will push the batter off. Spoon oil over for a few minutes. After about 4 minutes, use two spatulas to carefully flip relleno over. The batter may rip a little. Use a small spoon to push it back into place. Spoon some oil over the spots that need more browning. If the batter is cooking to fast, your heat may be too high. Temper the heat as needed. The rellenos cook for 8-9 minutes total time. Use the two spatulas to remove the relleno and transfer to a paper towel lined plate.
If you feel comfortable frying more than one relleno at a time, you can do that. Once the rellenos are all fried, pat off excess oil with paper towels. Naturally they will cool off as they sit there. You can transfer rellenos to a low temperature oven as you cook them, place them in the caldillo sauce on low to warm them before serving. You could also warm the rellenos by themselves in the microwave for 30-40 seconds. I like to ladle the hot caldillo over the top after warming the relleno. Serve with rice, beans and warm tortillas.