Heat a 12-inch skillet over medium-high heat. Working in batches, add chiles and cook, turning once until toasted, about 2 minutes. Transfer all chiles to a large bowl; pour over 4 cups boiling water, and let sit until chiles are soft, about 30 minutes. Drain, reserving 1 1⁄4 cups soaking liquid, and remove stems and seeds from chiles. Transfer chiles and reserved soaking liquid to a blender, along with garlic and onion; purée until very smooth, at least 2 minutes. Pour sauce into a bowl; set aside. Bring a 4-quart saucepan of salted water to a boil over high heat; add potatoes and cook until just tender, about 10 minutes. Drain and set aside. Heat 2 tablespoons oil in a 12-inch skillet over medium heat; add chorizo and cook, stirring to break up into small pieces, until browned and cooked through, about 8 minutes. Add potatoes and cook until potatoes are very tender, about 2 minutes; season with salt and pepper and set aside. Using your fingers, scoop out and discard the insides of rolls, leaving a 1⁄2-inch-thick shell. Place about 1 cup potato-chorizo mixture on roll bottoms, and cover with tops; press sandwiches lightly to flatten and compact filling. Heat 2 tablespoons oil in a 12-inch skillet over medium-high heat. Submerge two sandwiches in chile sauce until thoroughly soaked, at least 10 seconds; place in skillet and cook, pressing constantly with a metal spatula to flatten, and flipping once until browned on both sides, about 5 minutes. Transfer to a cutting board; repeat with remaining oil, sandwiches and sauce. Open sandwiches and divide lettuce, cheese and crema among sandwiches; close sandwiches again and serve warm.