Place the chiles colorados, tomatoes, and 2 garlic cloves in a medium saucepan. Cover with water and bring to a simmer over medium-high heat. Reduce heat slightly and simmer for 10 to 12 minutes until the chiles have plumped up and rehydrated, and the tomatoes are fully cooked and mushy. Transfer the chiles, tomatoes, garlic and a 1/2 cup of their cooking liquid to a blender. Add the chopped white onion, chiltepin chiles, chiles de árbol, oregano and salt. Puree until completely smooth.
Heat the lard or oil in a large heavy-bottomed pot or Dutch oven set over medium-high heat. Add the flour and stir together well to create a roux. Cook, stirring, for a minute or two until bubbling and lightly browned. Add the chile colorado puree. Cook, stirring often, making sure the mixture doesn’t stick and burn on the bottom of the pan, until it has thickened and darkened slightly, about 5 to 6 minutes. Stir in the beef broth and the shredded cooked meat and bring to a simmer, stirring. Reduce heat to medium, cover partially, and continue to cook, stirring often and scraping the bottom of the pot until the sauce has thickened and the meat is well seasoned, coated with the chile mixture, and so tender it is falling apart, about 30 minutes. Taste and adjust salt. Remove from the heat.