Heat large heavy skillet (cast iron) if you have one over medium high heat.
Season both sides of chuck roast with kosher salt and black pepper.
Lay roast in very hot skillet and brown on both sides for approximately 5minutes per side (until it gets a nice color). Leave it alone...don't move the roast around until ready to flip.
After you have seared the roast on both sides, place it in the bottom of large slow cooker.
Meanwhile, in food processor or large blender add all of the ingredients from garlic through beef broth.
Pulse in processor or in blender until everything is combine.
Pour sauce over roast.
Drop in bay leaves.
Fit slow cooker with lid and cook on low for 8 hours of high on 4-5.
Carefully remove roast from slow cooker.
Remove bay leaves from sauce and pour sauce into a container. Let sit for a few minutes so fat rises to the top.
While sauce is cooling for a bit, place roast back in slow cooker. Use 2 folks to shred the beef.
Skim fat off the top of the sauce. Add about 1/2 - 3/4 cup of sauce back into shredded barbacoa. You want it moist, but not swimming in sauce.
Serve as a filling for tacos, a salad or a Mexican style omelet.