1. Season the beef well with salt and black pepper. Set aside.
2. To roast the dried chiles (stemmed and seeded), if you have a deep, wide saucepan, you can use that to pan-roast and simmer the chiles in. Otherwise, you can roast them in a skillet (not non-stick), then transfer them to a medium to large saucepan. Heat the saucepan or skillet over medium-high heat, then add the chiles. Roast them, turning them so they don’t burn on any side, until they smell fragrant, about 3 minutes.
3. If using a wide saucepan, add the chicken stock. If using a skillet, transfer the chiles to a saucepan and add the chicken stock. Heat until the stock starts to boil, then reduce the heat and simmer until the chiles are completely soft, about 20 minutes.
4. Remove from heat and puree the chiles with the liquid using an immersion blender, being careful as the hot liquid can splatter, and stain. If using a standard blender, let the chiles and the liquid cool until room temperature, then puree until smooth. Do not puree the hot liquid in a blender as the top can blow off and cause injury.
5. To cook the beef, heat the oil in a large Dutch oven. Add as many pieces of beef that will fit in a single layer without crowding them. Depending on the size of your pot, you may have to brown them in batches. Sear the pieces of beef, turning them only as each side turns dark brown, until they’re browned on all sides. It’ll take between 5 to 10 minutes to brown each batch of beef. Once browned, remove the pieces of beef and put them in a bowl, then sear the next batch, adding more oil if necessary.
6. Once all the beef pieces have browned, and all have been removed from the pot, add the onions and garlic to the pot. (If there is too much oil in the pot after searing the beef, pour most of it out, leaving about a tablespoon in the pot.) Cook the onions and garlic, stirring, until they are soft and translucent, about 5 minutes. (If there is a lot of dark brown fond stuck to the bottom of the pot, add a few tablespoons of water and stir that into the onions. It’s a delicious addition.)
7. Add the cumin and coriander to the onions and stir for another minute, then add the chile liquid and brown sugar to the pot. Add the pieces of seared beef back to the pot, along with any liquid, and bring the beef in the sauce to a boil, then reduce the heat until the liquid is barely simmering.
8. Cover partially and cook until the beef is very tender, about 2 1/2 to 3 hours. Adjust the heat so the liquid is at a low simmer. While the beef is cooking, stir it a few times so the pieces are cooking evenly, and if necessary, add a splash of water or stock if the liquid has thickened and reduced too much before the beef is fully cooked. You can also taste the liquid and add more salt, if necessary.