Remove the thawed Bison Osso Buco from the Force of Nature packaging, pat dry with a paper towel, and season liberally with salt.
Add all the dried chilies to a skillet on medium heat and dry roast them for 2 minutes, until the skins darken.
Remove from heat and put the roasted chilies in a bowl of hot water for 20 minutes.
Using high heat, sear the top and bottom of the Bison Osso Buco in olive oil for 2 minutes per side in a large dutch oven and then remove from the dutch oven.
Lower the heat to medium, and add in the diced onion, and tomatoes, garlic and cook for 6 minutes.
Add the cooked onions, tomatoes, and garlic, ancho chilies, guajillo chilies, and arbol chilies to a food processor/blender.
Add the mexican oregano, cinnamon, cumin, ground ginger, apple cider vinegar and 1 cup of beef stock to the blender.
Blend on pulse until the texture is fairly thick.
Place the birria sauce into a bowl, add in the seared bison osso buco, and place into the refrigerator for at least 2 hours (overnight is better).
Heat up the dutch oven on medium high heat and add in the bison osso buco and birria marinade, diced tomatoes, the remaining cups of beef broth and cover.
Cook for 4 hours, or until the bison osso bucco is fork tender and easily shredded.
Add some additional beef stock or the water that the chile’s were soaking in for a soupier birria sauce & salt and pepper to taste.
Slice up the sourdough, drizzle with olive oil, and toast each side on a medium hot skillet until golden brown ~1 ½ minutes per side.
Assemble your sandwich by adding melted raw shredded cheese, shredded birria bison meat, chopped onion, and cilantro.
Pour some birria broth into a bowl, dip your sandwich in the broth and enjoy!