In a large, heavy skillet, heat the vegetable shortening over medium-high heat. Sprinkle the pork all over with salt and pepper. Sear the meat on all sides until golden brown, about 5 minutes per side.
Carefully add 3 cups water, the garlic, peppercorns, bay leaf and onion. Bring to a boil over medium-high heat. Cover, reduce the heat to medium-low and simmer until the meat is tender, about 25 minutes. Uncover and continue to cook until the liquid completely evaporates and the pork meat is browned, about 30 minutes.
Meanwhile, warm the refried beans in the microwave or in a saucepan over low heat.
Transfer the meat to a cutting board. Discard the garlic, peppercorns, bay leaf and onion. Thinly slice the pieces of pork.
Cut each bolillo in half lengthwise, spread 2 tablespoons of refried beans on each bottom half and top with 1/4 cup pork. Put the other bolillo half on top. Serve in shallow bowls and drench each torta with the warm Spicy Tomato Broth.
Combine the tomatoes, garlic, onions, oregano and chile in a blender and process until smooth.
Heat the vegetable oil in a medium, heavy saucepan over medium-high heat. Transfer the tomato mixture to medium, heavy saucepan and add the chicken broth. Bring to a boil. Reduce the heat and simmer until bright red, about 10 minutes. Season with salt and pepper.
*Bolillos are oblong-shaped individual rolls. Stale ones are perfect for these sandwiches because they soak up all great the tomato broth.
Recipe courtesy of Marcela Valladolid