Adjust an oven rack to 5-6 inches below the broiler and set the broiler to preheat.

Place the poblano peppers, tomatoes and onion on a large baking sheet lined with aluminum foil. Broil until the chiles and tomatoes are blackened and blistered on top and the onions are a bit charred, about 4-5 minutes. Carefully, flip the peppers, tomatoes and onions and broil until the surface is blackened and blistered.

Remove the onions from the oven and transfer them to a blender or food processor.

Return the baking sheet to the oven and keep broiling, rotating the peppers and tomatoes until blackened and blistered all over.

Transfer the tomatoes to the blender or food processor with the onions and add the jalapeno (if using) garlic, broth, and cilantro.

Wrap the poblanos with the aluminum foil from the baking sheet, or transfer them to a resealable bag to steam and sweat for about 5 minutes. This step is essential and makes peeling easy.

In the meantime, finish the sauce. Blend the roasted onions, roasted tomatoes, garlic, broth and cilantro until smooth (a few chunks is OK)

In a small saucepan, heat 1 tablespoon of oil over medium heat. Add the blended sauce ingredients into the hot oil (it will bubble up rapidly). Bring mixture to a boil.

Reduce the heat to low and simmer, stirring frequently for about 6-8 minutes or until the mixture has reduced by half. Season to taste with salt and pepper.

Carefully, peel the peppers without tearing them and removing as much of the skin as possible. It may help to rub off the skin with a piece of paper towel also.

Carefully, cut a slit down the middle of each pepper and remove some of the seeds. It doesn’t have to be perfect.

Divide the cheese among the 6 peppers and carefully, stuff the peppers. The peppers are delicate and may break up. This is part of the process. Do the best that you can. If some of your peppers are on the smaller side, you may have some cheese left.

Gently close the opening and secure it with toothpicks. Closing the pepper prevents the cheese from oozing out while frying.

Heat the oil in a deep skillet, saucepan or Dutch oven over medium-high heat until it reaches 375ºF(190ºC), adjusting the heat to maintain that temperature.

Line a baking sheet pan with paper towels for draining.

Place the egg whites in a large bowl and the yolks in a small one. Sprinkle some salt over the yolks. Using an electric handheld mixer, beat the egg whites until stiff peaks form. One at a time, add the yolks, mixing after each addition until the yolks are incorporated. Don’t overbeat. The mixture should be light and fluffy.

In a shallow bowl, mix together the flour and 1 teaspoon until well combined.

Gently, pick a stuffed poblano and roll it in the flour to coat. Tap each pepper gently to remove any excess flour.

Next, lift the flour coated pepper and dip it into the egg batter, rolling it so the batter sticks to the entire pepper. If the batter is not sticking evenly, spoon some of the batter over the peppers.

Carefully, slip the pepper in the hot oil. If you notice that some of the pepper doesn’t have much batter, simply spoon some over the pepper to coat.

Repeat the coating process and fry 2 to 3 peppers at a time to prevent overcrowding the pan.

Fry the peppers until the bottom is golden brown, about 2-3 minutes, flip the pepper to the other side and fry until the batter is golden brown and crispy, about 2-3 minutes. Transfer to the prepared baking sheet pan to drain. Repeat until all the stuffed peppers are fried.

Carefully, remove the toothpicks without breaking the pepper.

Spoon some of the sauce on a plate and place the chile relleno on top. Serve with a bit of sauce on top and crumbled cheese (such as queso fresco or cotija cheese)