Know that this soup, called a mole de olla (literally “soup pot mole”), isn’t a mole in the way we typically think of moles. It’s a brothy soup—almost a stew.
In a blender, combine the ancho powder, garlic, Worcestershire, 1 teaspoon salt and 4 cups water. Blend until smooth. (Mixture will keep in the refrigerator for 2 days.)
In a 6-quart slow cooker, layer the onion, potatoes, chayote and short ribs in that order. Pour ancho mixture into the slow cooker. Add the beer. The liquid should nearly cover the short ribs; if not, add more water.
Cover and turn on to high. Your mole de olla will be done in 6 hours, though you can hold it for longer.
When you’re ready to serve, place the green beans in a microwave-safe bowl. Sprinkle with a little water, cover with plastic, poke a few holes in the top and microwave on high until just tender, about 1 ½ minutes.
Scoop the short ribs out of the slow cooker. The meat will fall from the bones: discard the bones and tear the meat into bite-size pieces. Skim fat off the broth with a spoon. Stir the meat and green beansinto the soup. Taste and season with salt (usually a generous teaspoon).
Ladle into warm, deep bowls and carry to the table. Pass the lime wedges separately for everyone to add to their liking.
OVEN Variation: In a large (6- to 8-quart; at least 12-inches in diameter) heavy pot (preferably a Dutch oven) layer the ingredients as described in step 2. Bring to a gentle simmer over medium, set the cover in place and braise in a 300-degree oven 2 ½ to 3 hours, until meat is fork-tender, adding water occasionally if necessary to ensure the liquid stays at about the same level. Finish with the coarsely shredded meat and green beans as described in the recipe.