1. On a griddle or comal, roast Pasilla chiles for 10 minutes or until charred. Place them in a plastic bag and let them sweat for 5 minutes. Remove Pasilla chiles from plastic bag and peel. Remove seeds and veins.
Stuff each Pasilla chile with two Panela cheese slices and secure with a toothpick.
2. For the batter: Whisk egg whites until doubled in size, frothy, and white. Using a spatula, gently fold egg whites into egg yolks until completely incorporated. Season with salt and pepper.
3. Coat stuffed chiles with plenty of flour and dip in batter covering completely.
4. In a pot over medium heat, heat plenty of vegetable oil and deep-fry for 5 minutes or until golden brown. Drain on a paper towel-lined plate.
5. Serve battered chile Pasilla stuffed with Panela cheese with tomato sauce on top.