Cut chuck roast into 3-4 chunks and place into the crockpot.
Add onion, garlic, cinnamon, and bay leaves to the crockpot.
Drop in the birria bomb and pour beef broth over everything.
Cover and cook on low for 8 hours, until the beef shreds with zero effort.
Pull the beef out, shred it, and strain the consommé into a bowl.
Brush one side of each slice of sourdough with butter, then press the grated cotija into that buttered face.
Place the bread face down in a skillet, cotija side down.
Top each slice with oaxaca, American cheese, shredded beef, white onion, and cilantro.
Cook over medium-low heat until the crust is deep golden and lacy, flipping once, about 4 minutes per side.
Rest a minute, slice, pull, and dunk in warm consommé.