Place Hatch chiles on a foil-lined backing sheet and broil for 5-10 minutes or until the chile has dark black/brown blister spots.
Flip chiles and broil an additional 5-10 minutes until they are blackened on all sides. Carefully remove the peppers from the pan and place in a gallon-sized ziplock bag to steam (about 10-15 minutes). This helps it so the skin will easily peel away. Do not steam for more than 15 minutes or the pepper will become too soft and won't hold together.
Remove chiles from the bag and place on a cutting board. Remove skins from chiles once cool enough to handle.
Take each chile and slice a slit in the side with a sharp knife. Gently remove the seeds from each chile and then carefully stuff with cheese. Use 1-2 toothpicks to secure and seal.
Separate the eggs to make the batter. Place the egg whites in a mixing bowls and the yolks in a glass measuring cup.
Whip the egg whites on high speed until stiff peaks form. Reduce the speed to low and slowly add the egg yolks in. The batter should be light and foamy. Set aside.
In a separate, shallow dish, combie flour, 1 teaspoon salt and garlic powder.
Line up the chiles, flour mixture, and egg batter into an assembly line. Once oil is hot (350-degrees), dredge each chile in the flour then carefully dip it into the egg batter, covering it completely. Carefully place the chile in the oil and fry for 2-3 minutes or until golden brown on the bottom. Using metal tongs, carefully flip to the other side for an additional 2-3 minutes or until golden brown all over. Tip: Don't overcrowd your chiles rellenos in the frying pan or deep fryer. I usually fry in batches of 2 (mostly because my pan is so small).
Remove chiles rellenos from the oil and place on paper towels to drain. Serve hot.
Serve with red sauce (see instructions below), salsa verde, and/or Mexican crema.