Special equipment: Tamale corn husks: 24 enconchada dried corn husks such as those marketed by Corona Real or 48 to 72 standard dried corn husks (an allowance of 2 to 3 husks per tamale), or fresh corn husks (as is the custom in some Latin American countries) boiled water poured over them and allowed to soak for 30 minutes
For the buffalo: Season buffalo meat with salt and pepper. In a large stockpot, cover buffalo meat with water, add onion, garlic, chiles and cumin. Cover and bring to a simmer. Slowly braise for about 2 hours or until the meat is fork tender. Reserve cooking liquid for the sauce.
For the corn husks: Place the corn husks in a large bowl and cover with tepid water. You may have to weigh them down with another bowl of water. Allow to soak as needed to hydrate, while the buffalo is braising.
For the masa de maez: Melt 2/3 cup of the shortening in a saucepan and set aside. With an electric mixer, beat the other 1 1/3 cups of the shortening until fluffy and gradually and alternately begin adding the harina and beef stock, mixing well after each addition. Then gradually add the melted shortening mixing completely after each addition. Cover the bowl of dough with a damp kitchen towel and set aside.
Transfer the buffalo meat to a utility platter and shred with 2 forks. Reserve 2 cups of the cooking liquid for the sauce. (If there is not enough, don't worry, you will supplement it with beef stock for the sauce.) Leave enough of the cooking juices to keep the meat just moist and return the shredded beef to this liquid, and cover to keep warm.
Lay out the corn husks and spread about 1 to 1 1/2 tablespoons of the masa dough into each followed by 1 to 2 tablespoons of the shredded buffalo. Fold each tamale so that the masa encases the meat, and use a thin strip of corn husk to tie the tamale. Place in a steamer basket, on end if possible, so that each tamale supports the one next to it. Place over a pot filled with a couple of inches of simmering water for steaming, cover and let steam until firm, about 1 hour. (The corn husk will fall away easily when it is done.
While the tamales are steaming, make the tamale sauce. Heat the grapeseed oil over medium to medium high heat in a medium saucepot. When the oil begins to shimmer add the shallots and garlic and saute until the onion becomes translucent. Add 2 cups of the buffalo cooking liquid and/or beef stock to the shallots and garlic and increase heat to bring to a rapid boil. Add the chili powder, salt and pepper, to taste, and let reduce by half. Add the cornstarch to a separate small bowl and gradually whisk in 1 tablespoon of the liquid to create a slurry. Gradually whisk this into the saucepot to thicken the mixture.
Let tamales rest briefly before serving, and serve with small bowls of tamale sauce.