Remove the tops of the dried peppers with scissors and empty out the seeds. If you like it extra spicy, leave the seeds in.
Rehydrate the dried peppers by putting them in a bowl and covering them with boiling water. Let them soak for at least 10 minutes. (If you plan to make the salsa, you can soak all 8 peppers now).
Cut the meat into small cubes and mix with spice rub. If you plan to cook this now, season the meat with about 1 tsp of salt.
Make the adobo sauce by blending all of the ingredients for the sauce together with the 4 hydrated peppers. Blend with the pepper soaking water.
If you are marinating overnight, let this sauce cool completely before adding it to the meat. Cover and let sit in the fridge overnight.If you plan to make this now, add this sauce to the seasoned beef and mix. Add to this to Instant Pot. Close the Instant Pot lid and set the timer for 40 minutes on high pressure. (If using a Dutch Oven or Slow cooker see above for the method) Optional: While the meat is cooking, make the chili salsa by frying the tomatoes, onions and garlic over low heat in a cast iron pan for about 5 minutes.Add this plus the rest of the ingredients for the salsa to the blender and blend until smooth. Now is a good time to prepare the other taco accompaniments (guacamole, cheese, onions, herbs, etc). Once the timer goes off for the Instant pot let it naturally release for 10 minutes and manually release the rest. Let the beef sit in the broth for about 10 minutes to allow the fat to rise to the top.
Remove the beef from the broth with a spider strainer and shred with a fork.
To make the tacos, dip the tacos in the beef fat on the top of the broth, and fill them with the braised meat, salsa and cheese if desired.
Fold them in half and fry them on both sides on low heat until golden brown.
Serve right away with your favourite taco accompaniments and the hot broth on the side to dip the tacos in. Enjoy!