Into the bottom of a slow cooker or crockpot, place the sliced red onions, three large bay leaves, and one ancho or poblano pepper.

Cut the meat into large cubes and pat dry, then set aside.

Place a large skillet over medium-high heat and add two tablespoons of oil; once the oil is hot, sear the cubes of meat for one or two minutes per side, use a pair of tongs to move the meat around. You will have to do this in batches, only adding two or three meat pieces at a time. After you have browned the pieces on all sides, place the seared cubes of beef into the slow cooker or crockpot.

Into a food processor, add the ground cumin, chipotle in adobo sauce, dried oregano, smoked paprika, tomato paste, garlic cloves, beef stock, Mexican beer, and fresh lime juice. Purée the mixture for one minute to make a barbacoa sauce.

Pour the barbacoa sauce over the seared beef pieces in the slow cooker or crockpot. Use a pair of tongs to move the pieces around to make sure they are evenly coated.

Place the lid on the slow cooker or crockpot and cook for eight (8) hours on low.

When the meat is finished cooking, remove the lid and use a pair of forks to shred the beef. Use a pair of tongs to stir the shredded Barbacoa into the drippings. Place the top back onto the slow cooker and allow the meat to steep for ten (10) minutes.

Serve.