If you’re using the oven, turn the broiler on high and put the poblano peppers on a baking sheet and place them in the oven. If you’re using the stove, place your peppers on a comal over medium high heat. Turn the peppers once they start to develop char marks. Keep turning them until each side has char marks.
After each pepper is roasted on each side, place them in a paper or plastic bag, close it and let it rest for 10 minutes or until you’re able to handle them.
Peel off the thin film on each pepper. Do NOT rinse them under water. Doing so will remove the flavor of the roasted poblano.
With a paring knife cut a small slit in each pepper. Remove the seeds. Be careful not to make the slit too big or the pepper can fall apart when adding cheese.
Carefully stuff each pepper with cheese and using a toothpick close the slit. Set aside.
In a large bowl, add the egg whites and using an electric hand mixer whisk the egg whites until you have stiff peaks. Then add the egg yolks, salt and flour and mix until incorporated. Set aside.
Add flour to a plate and season with some salt. Set aside.
In a pan with high sides, add enough oil so you can pan fry the peppers. Heat up the oil over medium high heat.
Take a pepper and gently roll it in the flour. Patting off any extra flour then dip it in the fluffy egg batter and then into the hot oil. Cook for 3-4 mins on each side or until golden brown. (Use an extra utensil to help flip it over so you don’t splash oil all over.) Place on a plate lined with paper towels to absorb any extra oil.
When serving you can place a chile relleno on a plate and ladle some of the tomato sauce all over or even place the chile relleno in the sauce for a minute before serving.