Prepare Beef: Trim exterior fat from beef, then cut beef into 2-inch chunks (Note 3). Place chunks along bottom of slow cooker.
Blend Sauce: Blend all sauce ingredients in blender (Note 4) until combined, about 20 seconds. Pour sauce over beef chunks in slow cooker, and use tongs to mix until well-coated.
Cook & Shred: Cover and cook on low heat for 8 hours. Transfer only meat to large bowl, and shred using two forks.
Optional Sear: Transfer shredded meat to large sauté pan (Note 5). Flipping meat frequently, cook over medium-high heat until browned with crispy bits, about 5 minutes.
Serve: Soak shredded meat with some or all of liquid from slow cooker, as desired; stir in a small amount of liquid at a time, until meat has desired consistency (Note 6). Serve and store any leftovers (Note 7).
