Preheat oven to 350
Remove stems and seeds from chiles and put into a blender, add the boiling broth and cover
Meanwhile, season the beef well with salt & pepper, and sear in 2 batches in a hot oven proof pot - remove to a plate and repeat with remaining beef
To the empty pot, add the onions with a little more oil and cook until softened, about 5 minutes
Add the vinegar, scraping up the bits on the bottom and allow about ½ of the vinegar to evaporate - then add garlic and when fragrant, about 45 seconds later add the beef back in and take off the heat
To the softening chiles add the oregano, cumin, coriander, chipotles, salt & pepper and diced tomatoes
Blend until very smooth and pour over beef in pot - the beef should be covered and if not add a little more broth
Cover, and place in the oven until fork tender and shredable - approx 2 to 2.5 hours
For tacos: dip a tortilla in some of the cooking liquid and place on flattop and when it starts getting a little brown, add some beef and shredded cheese, fold over and cook until getting crispy on both sides
Remove, open up carefully, add onions and cilantro and eat
Go make another 10
