Prepare meat. Stovetop method: Add meat to a large pot with 1 onion peeled and cut in half, 3 cloves garlic, peeled and smashed and 1 tablespoon salt. Add enough water to cover the meat by three inches and then bring to a boil and cook until tender, about 2 to 2.5 hours. Crockpot method: Add meat to a large pot with onion, garlic, and salt. Add enough water to cover the meat by three inches and then set on low for 10 hours. Once meat is cool, cut into 1.5inch slices going against the grain and then shred by hand. Set aside.PRO TIP: You can prepare your meat a day in advance.
Prepare chili peppers. While meat cools, you can prepare the remainder of your ingredients, beginning with the chili peppers. First, toast chili peppers over an open flame on the stove until blistered all over. Next, add peppers to a bowl that’s lined with a plastic produce bag. Cover chiles with the plastic bag and allow them to sweat inside the bag for at least 15 minutes. Remove charred skin by scraping it off with a dull knife. Once you have removed the skin, slice or chop the peppers to your desired size. Sometimes I leave them in rajas (thin strips), other times I chop them into smaller pieces.PRO TIP: You may want to use gloves for this step if you’re sensitive to chili peppers.
Prepare the remainder of your ingredients. Chop tomatoes. Slice remaining onion into thin half moons.
Saute ingredients. Heat pan and once it's hot, add 3 tablespoons cooking oil. Add onion and tomato and cook until onion becomes translucent, for about three minutes. Next, add chili peppers and meat. Sauté for an additional 15 minutes. Taste and adjust salt, if necessary. Cover, lower heat, and simmer for at least 30 minutes to allow flavors to meld together. PRO TIP: For a juicier meat, add one cup of the beef broth before covering.