How to Make It
Preheat oven to 400°. In a molcajete (volcanic stone mortar), grind the garlic clove with a little olive oil and black pepper to create a smooth rub. Place the pork loin on a baking dish and evenly spread the rub over the pork. Allow to marinate for 1/2 hour. Mix the coarse salt with 1/2 cup water to produce a rough paste. Spread the paste over the pork loin and bake for 1 hour, or until the meat is tender but cooked. Remove the pork loin from the oven and allow the meat to stand for 1/2 hour. Remove the layer of baked salt on the surface of the pork and cut into thin slices.
Place the water in a medium saucepan and bring to a boil. Add the fresh and dried arbol chiles, garlic cloves and onion to the pan and cook for 10 minutes. Remove from heat and transfer the chiles, garlic and onion to a blender or food processor and puree along with 1 cup of the cooking water. Add the vinegar and the roasted peanuts and puree until a smooth sauce forms. Season with salt and pepper.
Preheat a heavy comal or frying pan. Roast the tomatoes until the skin is charred. Carefully peel the charred skin off the tomatoes. Roast the onion and garlic at the same time until lightly charred. Place the chiles on the comal or in the frying pan and sprinkle with the olive oil. Roast the chiles until very lightly browned; be careful not to char the chiles or they will give the salsa a bitter flavor. Place the roasted tomatoes, onion, garlic and chiles in a blender or food processor. Add the raw onion, reduced broth and vinegar and puree. In a molcajete, grind the oregano leaves and cumin seed by hand and add to the salsa. Season to taste with salt and pepper.
Heat a cazuela (clay pot) and add the olive oil. Transfer the pureed salsa to the cazuela and cook for about 10 minutes, or until the sauce is thickened.
In a pressure cooker, combine the water, onion, garlic, soaked beans and salt. Cook for 45 minutes. Remove from the heat and allow the pressure to drop before removing lid.
Mash the beans until they form a thick puree. Heat a medium-large frying pan. Add the oil and sauté the slice of onion until golden brown. Add the beans and cook over medium heat. Season with salt and pepper.
Slice the rolls open and remove the dough in the center. Spread the bread with the refried beans. Place a slice of pork loin in the middle of the sandwich. Transfer the sandwiches to a platter or plates and serve with the peanut sauce and the tomato-chile arbol sauce.