Pour the beer into a sauce pan over medium heat. Break up the chipotle and arbol chiles with your hands into smaller pieces, removing most of the seeds and stem. Put a small frying pan over high heat and add the chiles. Cook for a minute or two until fragrant. Pour this mixture into the beer. Bring to a simmer and cook for 2 minutes, then cover and remove from heat. Allow to sit for a half hour.
Put a large pot over high heat, or set a slow cooker to “saute” mode. Season the beef and lamb well with salt and pepper. In batches, brown the beef and lamb on all sides. Make sure you do this in smaller batches, not crowding the pan, to make sure to get some good browning. As each batch is done, remove to a large bowl, leaving the fat in the pot.
Add the onions and poblanos to the pot with the fat when the meat is done. Season with salt and pepper. Cook for about 7-8 minutes until softened and slightly brown on the edges. Add in the garlic and cook another 2 minutes, stirring often.
Add in the tomato, chili powder, berbere, cumin, paprika, oregano, bay leaves, coriander, clove, allspice, vinegar, sugar, and worcestershire. Stir to combine. Season with salt and pepper.
Use a blender or hand blender to blend the beer-chile mixture until fairly smooth with no large pieces. Pour this mixture into the pot with everything else.
Cover and cook at a light simmer for about 4 hours until the lamb is falling apart. Add in the beans and cook another half hour.
Taste, and adjust seasonings to your personal taste. I added a pinch of allspice, oregano, and a little more vinegar and salt at this point.
Serve with sour cream, cilantro, and scallions.