Step 1: Make the Chili Paste

1. Remove the stems and seeds from the dried guajillo and ancho chiles.
2. Bring the beef stock to a boil in a medium pot. Add the chiles, cover, and let them sit for 15-20 minutes until softened.
3. Transfer the softened chiles to a blender or food processor along with the remaining chili paste ingredients. Blend until smooth and thick, adding more beef stock or water if needed.

Step 2: Cook the Meat

1. Preheat the oven to 350°F (175°C).
2. Heat olive oil in a Dutch oven over medium-high heat. Sear the beef chunks on all sides for about 3-4 minutes each.
3. Remove the beef and set aside. In the same pot, sauté the onions until fragrant and translucent (1-2 minutes).
4. Stir in the chili paste and let it simmer for 1-2 minutes.
5. Add the beef stock, water, and seared beef. Stir well and bring to a simmer.

Step 3: Braise in the Oven

1. Cover the Dutch oven and transfer to the preheated oven.
2. Cook for about 2½ hours, or until the beef is tender and easily shredded.
3. Remove from the oven and shred the meat, keeping it in the sauce for maximum flavor.

Step 4: Assemble the Tacos

1. Remove 1 cup of the broth from the pot and place it in a small bowl. Sprinkle with fresh cilantro for the dipping sauce.
2. Heat a non-stick skillet over medium heat and add 1 tablespoon of olive oil.
3. Dip a tortilla into the reserved broth and place it in the skillet.
4. Add shredded beef, diced onions, chopped cilantro, and shredded cheese.
5. Fold the tortilla in half and cook until crispy and golden on both sides, about 1-2 minutes per side.
6. Repeat until all tacos are made.