Start by toasting the guajillo and ancho chilies in a dry skillet over medium heat for about 2 minutes, until fragrant. Remove from heat and let them cool slightly.
In a blender, combine the toasted chilies, quartered onion, garlic cloves, ground cumin, oregano, smoked paprika, and a pinch of salt. Add about 1 cup of beef broth and blend until smooth.
In a large pot or Dutch oven, heat a tablespoon of oil over medium-high heat. Season the beef and lamb chunks with salt and pepper, then brown them in batches, making sure not to overcrowd the pot.
Once all the meat is browned, return it to the pot and pour the blended chili sauce over the meat. Add the remaining beef broth and bring to a boil. Lower the heat to a simmer, cover, and cook for about 2 hours, or until the meat is tender and easily shreds.
Once cooked, remove the meat from the pot and shred it using two forks. Strain the remaining broth to separate the solids and keep the delicious consomé for dipping.
To make tacos, heat the corn tortillas in a skillet over medium heat until pliable. Dip each tortilla in the consomé, then fill with shredded meat, and fold.
Serve the tacos with chopped cilantro and lime wedges on the side.
Notes
Serve the tacos on a rustic wooden board with a small bowl of consomé for dipping, garnished with fresh lime and cilantro.