Place the pork tenderloin and bay leaf in a slow cooker; pour the beer over the meat. Cover and cook on low until well cooked and the pork shreds easily, 6 to 8 hours. Discard the bay leaf. Remove the pork from the slow cooker and shred the meat. Set aside for assembly.
Arrange tomatoes and tomatillos on a baking sheet. Place your oven rack as close to the broiler as possible. Broil the tomatoes and tomatillos for about 10 minutes until softened, turning over after 5 minutes. If the skins have blackened remove them.
In a blender, puree the roasted tomatoes and tomatillos, canned diced tomatoes, chipotle peppers with adobo sauce, tomato sauce, chopped onion, garlic, flour, and water until smooth.
Heat olive oil in a large skillet. Pour in blended sauce carefully to avoid too much splatter and bring to a boil. Lower heat and simmer for about 10 minutes.
Taste and season with salt, usually about 2 teaspoons. If sauce is too spicy, add an additional can of tomato sauce and stir. If sauce is too thick, add water until desired consistency is reached, making sure to add more salt if necessary.
In a large skillet, heat canola oil until hot. Fry tortillas until softened. Drain on paper towels. Place lightly fried tortillas, one at a time, in the skillet of warm red sauce, turning to coat.
Place a coated tortilla on serving plate. Layer the chile-coated tortilla with some shredded pork, diced onion, and crumbled cheese. Place another coated tortilla on top and repeat layering until the stack has 3 tortillas. Continue making stacks until all tortillas are used. Serve each stack with a dollop of crema or sour cream.
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