For the sauce:
1/2 small onion, chopped
2 cloves garlic, minced
1 tbsp chile pepper
2 tsp ground cumin
1 (8 oz) can tomato sauce
1/2 cup chicken stock

Bring a small saucepan of water to a boil. Add the potatoes and cook until fork tender, about 15 minutes. Drain thoroughly, place in a large bowl, and set aside.

To make the sauce; combine the onion, oil, and 1/2 teaspoon salt in a large saucepan. Cover and cook over medium-low heat, stirring often, until the onions have softened, 8 to 10 minutes. Stir in the garlic, chili powder, and cumin; cook until fragrant, about 30 seconds. Stir in the tomato sauce and water, bring to a simmer, and cook until thickened, about 10 minutes. Remove from heat, and strain sauce through a fine mesh strainer. Set aside.

Make a slit down one side of each pepper. Place them in a dry skillet over medium heat, turning them frequently until the skins blister. Place the chiles in a Ziploc bag and seal closed to steam peppers. Set aside for 20 minutes, then carefully peel off the skins and remove the seeds, if desired, keeping the chiles whole. Dry the chiles with paper towels and set them aside.

Put the cream cheese and shredded cheese in the bowl with the potatoes. Add salt and pepper, and mix to combine. Spoon some of the potato filling into each chile, and squeeze it back closed.

In a standing mixer fitted with a whisk attachment, whisk the egg whites to firm peaks. In a separate bowl, whisk the egg yolks until pale, then fold in the egg whites. Scrape the mixture onto a large, shallow dish. Place the flour in another shallow dish and season it with salt.

Add 1/2″ oil to a heavy bottomed skillet and heat to 375. Coat a few chiles first in flour and then in egg before adding carefully to the hot oil. Fry the chiles in batches until golden and crisp. Drain on paper towels. Serve on a bed of chile sauce, with some sauce drizzled on top as well.

Source: adapted from The Complete Mexican, South American & Caribbean Cookbook