Remove stem end of chile, then insert knive through opening to remove seeds and ribs (Alternatively if you want to leave the stem attached, you can make a “T” shaped cut with the top of the “T” at the stem end of the pepper to remove the seeds and ribs).
Place chile(s) on aluminum foil under broiler. Broil, turning occasionally with tongs, until the chile blackens and blisters on all sides. Watch carefully–peppers are flammable! Roll up the chile in the foil and allow to steam until tender and cool enough to handle, about 10 minutes. Peel/scrape away the blistered skin, being careful not to tear the flesh.
Fill the chile with grated cheese. Set aside.
Beat the egg whites and salt on high speed until stiff peaks form. In a separate bowl, beat the egg yolk until frothy. Fold the beaten yolks into the whites until just combined, trying to deflate as little as possible.
Heat the oil in a large frying pan over medium heat until hot.
Now here my version is slightly different than many others, in an approach that I think is a bit easier (and also lower carb. Instead of dipping the stuffed pepper in flour, then egg batter, and then moving the drippy pepper to the hot oil, I do the following:
Drop about 1/2 cup of batter into the oil and spread it to about the same size as the stuffed chile. Let it cook for a few seconds to firm just slightly.
Gently, lay the chile on top of the batter in the pan. Spread remaining batter over the chile to cover it on all sides. Cook without disturbing until the bottom of the chile relleno is golden brown. Using a flat spatula and a fork, carefully flip the chile relleno over and cook until the other side is golden brown (sometimes I’ll brown on three sides, depending on the chile’s shape).
Warm salsa if cold. To serve, spread 1/3 cup of salsa on a plate and top with the chile relleno. Or serve the salsa on the side. Serve immediately.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.