Masa-Thickened Beef Soup with Chiles

Beef is butchered differently in southern Mexico than in the U.S. or even the north of Mexico, where I grew up. In Oaxaca, when all the important cuts have been taken from the carcass, various hunks of bone with meat attached remain for sale—very daunting-looking as they hang over the flyspecked butcher stalls that are a village’s usual source of meat. These pieces of bone with irregular leavings of meat are appropriately called retazo, which means odds and ends of something (like fa