Put the meat into a heavy pot with water to cover and salt. Cover and cook over medium heat until tender-about 1-1/2 hours, depending on the quality of the meat. Reduce the broth over high heat or add water to make 6 cups. Put 1 CUP aside for the masa.

Put the unpeeled garlic and the onion onto an ungreased comal or griddle and cook until the garlic is soft and the onion slightly charred but translucent. Peel the garlic and set aside.

Put the tomatoes and tomatoes verdes onto the comal or griddle or under the broiler and cook until soft and slightly charred. Transfer to a blender.

Lightly toast the whole chiles on a comal or griddle, rinse briefly, tear into pieces, and add to the blender with the peeled garlic and onion, then blend until smooth. (If you're using puyas, remove the seeds and veins before toasting and soak for about 10 minutes, then blend separately and pass through a strainer before adding to the rest of the ingredients.) Add the blended ingredients to the 5 cups of broth.

Put the separate cup of broth into the blender, add the masa, and blend until smooth. Stir into the other broth mixture. Cook over low heat until the sauce thickens slightly, taking care not to let it stick to the bottom of the pan.

Add the meat and epazote and cook, still over low heat, for about 5 minutes.

Serve in warm bowls.