For the braised pork butt: Preheat the oven to 325 degrees F.
In a small bowl, combine the chili powder, cumin, garlic, paprika, mustard, coriander, salt and pepper. Pat the pork dry, then coat it with the rub.
In a large cast-iron pan, heat the canola oil over medium-high heat. Sear the pork until browned on all sides, 8 to 10 minutes. Pour in the beer, cover the pan tightly with foil and transfer it to the oven for 2 1/2 to 3 hours. Let the pork cool a bit before shredding.
For the tomato sauce: Soak the chile de arbol for 20 minutes in warm water. Once rehydrated, remove the stems and seeds and roughly chop. Heat the canola in a medium saucepan over medium heat. Add the onion and saute until translucent, 5 to 7 minutes. Stir in the chile de arbol, jalapeno, garlic, cumin and oregano and cook for another 2 to 3 minutes, until fragrant. Add the vinegar, tomatoes and 1 cup water. Bring to a simmer and cook for 45 to 50 minutes, stirring often. When done, puree the sauce until smooth. Season with salt and pepper to taste.
To assemble the sandwich: Slice the bolillos in half, leaving them hinged at one end. Brush the insides with olive oil. Place the bolillos cut-side up on a baking sheet; transfer to the oven and toast until crispy, about 5 minutes. Fill each bolillo with some shredded pork, topped with some tomato sauce, shredded cabbage, cilantro, pico de gallo and pickled red onions. Serve.
Pico de Gallo:
In a bowl, combine the tomatoes, jalapeno, lime juice, red onion, cilantro and garlic. Mix to combine. Season with salt and pepper, and refrigerate for 1 hour to allow flavors to meld.
Pickled Red Onions:
Heat a small saucepan over medium heat. Add the olive oil, the onions and some sea salt, and saute until the onions are just softened, about 5 minutes. Add the bay leaf, cayenne, cinnamon, start anise, honey, red wine vinegar and just enough water to cover. Bring to a boil, then turn off the heat. Set aside to cool to room temperature. Remove the whole spices and refrigerate until ready to serve.
Bolillo rolls, 6-inches long and football-shaped, are traditional in tortas. If you cannot find them, substitute French rolls of roughly equivalent size and shape.