For the Guajillo Salsa
Heat a large, dry frying pan or comal over medium-high heat. Add the 4 guajillo chiles and 4 arbol chiles, 2 cloves unpeeled garlic, and 1/2 white onion, quartered. Watch vegetables closely, turning as they toast.
Remove the chiles to a plate as soon as they are toasted and fragrant so they don't burn. Garlic will also be done before the onion, then finally the onion, which will take about 10 minutes to char on all sides.
Bring a medium saucepan of water to a boil. Add toasted chiles and submerge under the water. Remove pan from the heat and let chiles soak until tender, about 15-20 minutes.
Remove chiles from the water and add to a blender, along with charred onions. Peel the garlic and add that as well, along with the 1/2 teaspoon oregano, 1 teaspoon cumin, 2 teaspoons apple cider vinegar, 1 teaspoon salt, and 1 teaspoon brown sugar.
Add 3/4 cup of the chile-soaking water and blend until smooth. Taste and add more salt if needed.
Pour into a shallow dish and set aside.
For the Filling1. Heat the tablespoon of sunflower oil l in a medium frying pan over medium heat. Add the diced potato and the 1 teaspoon kosher salt. Stir to coat in oil and let cook, stirring occasionally, until starting to become golden brown.
2. Add the pound of chorizo, breaking up with a wooden spoon. Cook 2-3 minutes or until the chorizo starts to firm up.
3. Add the onion and continue cooking until the onion and potatoes are tender. Check the potato with a fork, it should go through easily. If the potatoes are getting too dark but not tender, cover the frying pan, lower the heat and continue cooking.
4. Once potatoes are cooked through, cover and keep warm.
For the Tortas1. Slice 4 rolls in half, dip the outside (the crust side) of each roll in the sauce. Set on a baking sheet or large plate.
2. Heat 2 tablespoons of the sunflower oil in a separate large frying pan over medium heat. Once the oil is hot, place bread in skillet, sauce side down. Fry in batches until golden and crisp on both sides, about 3-4 minutes. Press down on the rolls to get them really nice and crisp.
3. Repeat with the remaining rolls, adding 2 more tablespoons of oil to the frying pan with each batch.
4. Divide the filling and toppings evenly among the rolls. Cut in half and serve.