Prepare The Pepper Puree
In a sauce pan, combine two cups of beef broth, one onion, three ancho chili peppers with stems removed, cumin seed, garlic and cilantro. Cover the pan and cook on medium heat until the onions are soft. Then use a blender to puree the contents of the pan.
Cook The Roast
Place the chuck roast in an oven safe pan with a lid. A crock pot can also be used. Pour the chili puree over the top of the roast and cover with a lid. Place the pan in the oven at 250 degrees or into a crockpot on low. Cook for 5 hours, or until the meat easily pulls apart with a fork. Halfway through cooking, flip over the roast to coat both sides with juices.
Prepare The Mesa Mash
In a sauce pan, combine 1 cup mesa flour, and 3 cups beef broth. Cook until the corn is soft and resembles mashed potatoes. Before serving, add 1/2 cup sour cream. Serve warm.
Serve the shredded beef over a bed of mesa mash. Tastes great topped with guacamole, salsa and romaine lettuce.