Red Chile Shortrib Soup - Rick Bayless

Ingredients

• 1 medium white onion
• 1 pound small red- or white-skin boiling potatoes (I like ones that are about 1 inch across; if they're larger I cut them into halves or quarters)
• 1 large chayote, peeled if you wish, seed cut out, flesh cut into 1-inch pieces
• 4 pounds (about 6 pieces) bone-in English-cut (that is, cut parallel to the bone) short ribs
• 1 1/2 ounces dried chiles (roughly 6 guajillos, 4 to 5 pasillas or 3 anchos), stemmed, seeded and torn into 2-inch pieces
• 4 garlic cloves, peeled and halved
• 1 tablespoon Worcestershire
• Salt
• 1 large sprig epazote, if you have it
• About 6 ounces green beans, stemmed and cut into 1-inch lengths
• 2 or 3 sour prickly pear cactus fruits (xoconostles), if you have them
• 1 large lime, cut into wedges