Place peppers on baking sheet and place under broiler. After 5 minutes, flip over and broil for another 5 minutes.
Let the peppers cool for a couple of minutes and place in a plastic bag, covering completely to release steam. Leave in bag for 5-6 minutes.
While the peppers are in the bag, place a large pan over medium heat.
Remove the peppers from the bag and peel off as much of the skin as possible. You can also run the peppers under cold water to make peeling easier. Do not worry if not all of the skin comes off, some intact is just fine.
Gently cut a slit in pepper from the stem to the end, ensuring the pepper stays in tact and you do not cut through the entire pepper. This will create a pocket for the stuffing. Remove the seeds and veins from pepper as much as possible. Stuff peppers with filling of choice just until pepper is full and still able to close at opening.
Add oil to pan that is on medium heat.
Place flour on a large plate or sheet pan and coat stuffed peppers with flour by gently rolling peppers in flour, making sure stuffing stays in place. This will ensure egg batter adheres better.
In a large mixing bowl add egg whites and salt and beat until stiff. Add yolks and beat only until incorporated.
Dip the peppers one at a time into the egg batter, coating them completely. After the pepper has been dipped, immediately place pepper onto hot pan. Don't overcrowd the pan as to not lower temperature of oil too much.
Pan fry until they start to get golden around the edges, about 3 minutes, and carefully flip and continue cooking until golden on all sides. If there are areas that are not being cooked in the oil, use a spoon to obtain some of the hot oil from the pan and spoon oil over those areas to cook.
Once peppers are cooked place them on a sheet pan or large plate lined with paper towels to drain.