Put guajillo and arbol chiles in a cast-iron skillet over low heat and toast, turning often, until lightly toasted and fragrant, 1 to 5 minutes depending on how brittle they are. Remove stems from chiles, cover with hot water, and let soak 15 to 20 minutes.
Meanwhile, lift beans from broth with a slotted spoon to a deep bowl, reserving broth. Add salt to beans. Using a pastry blender, potato masher, or machacadora*, mash beans into a coarse paste.
Drain chiles and put in a blender. Add cumin and 1/3 cup bean broth; blend, scraping down inside of blender a few times, until chiles are coarsely puréed and pourable. Add more broth if needed.
Pour chile purée into beans and mix thoroughly into a thick but creamy-looking paste; add more broth if needed to loosen. Season with salt to taste.
Put lard in a medium (not nonstick) frying pan and melt over medium-low heat. Add chile-bean paste and fry, stirring, 5 minutes to blend flavors. Cool 15 minutes.
Meanwhile, if using corn flour, put it in a large bowl. Drizzle in 1 1/3 cups hot water while kneading it into the flour with your fingers. Knead until dough is smooth, moist, and no longer sticks to your hands. If it feels dry, knead in a little more water; if it's sticky, work in a little more corn flour. Keep masa covered with a damp kitchen towel as you use it, since it dries out quickly.
Put a serving platter into a 200° oven to warm. Heat a large cast-iron skillet or griddle over medium-low heat.
Meanwhile, line both inner sides of a tortilla press with a piece of plastic, cut from a resealable bag, to be about the same diameter as the press. Pinch off a ball of masa (about 1 1/2 in. wide) and enclose it in your palm, squeezing your fingers over it to form it into a cigar shape. (It should just fit in your folded hand; if your fingers can't fit over it, remove some masa.) Shape cigar into a cylinder about 3 1/2 in. long and tapered at the ends.
Set masa cylinder inside tortilla press and parallel to the handle. Use the press to flatten it until it's about 1/4 in. thick. Rotate 180° and press again to flatten a little more.
Fill oval with about 1 tbsp. bean paste, spooning it down center. Using bottom plastic wrap to guide the soft masa so it doesn't stick to your fingers, bring both long sides of oval up to meet over filling; then fold them to one side over filling. Gently push ends of masa oval into points. With plastic over it, flatten the filled oval with your hands to about 1/4 in. thick. Peel plastic off masa and put tlacoyo in skillet.
Repeat with remaining dough and filling, adding each tlacoyo as formed to skillet. Toast them until golden brown with some darker spots, about 2 minutes per side, then transfer to platter in oven to keep warm, covered with foil.
Top with queso fresco and salsa.
*Buy this cool, moist, fresh corn dough (not to be confused with "masa preparada" or "masa para tamales," which are coarser) at Latino markets. Or, use masa harina (powdered masa) for tortillas, reconstituted with water as directed in step For tastier, properly crumbly cheese, take the queso fresco out of its package a day beforehand, blot it, and let it dry out overnight (or even 2 nights), uncovered, on a plate in the refrigerator. A machacadora is a Mexican-style bean masher; find one at ranchogordo.com or Latino markets.
Make ahead: Freeze airtight up to 1 month.