Heat a large pan to medium heat and add the dried peppers. Dry toast them in the hot pan 1-2 minutes per side, until the skins darken.
Remove from heat and add the toasted peppers to a large bowl. Cover with hot water and steep 20 minutes, or until softened.
While the peppers are rehydrating, heat the olive oil in the same pan to medium heat.
Add the onion cook for 5 minutes to soften.
Add the garlic and cook another 1 minute, stirring. Add canned tomatoes and cook another 5 minutes.
Add mixture to a food processor. Puree.
Remove the softened chilies from water and add to the food processor. Puree.
Add the seasonings to the food processor along with the vinegar and 1 cup beef stock. Process until smooth. Strain if desired to remove any unprocessed bits of skin.
Cut the beef into large chunks and sear in a large stock pot 3 minutes per side.
Add birria sauce to pot. Add remaining 3 cups beef broth. Cover and cook at medium heat for 3 hours, or until the meat is fork tender and easy to shred. It should be fairly saucy. Shred the meat with forks to your preference.
Toast tortillas straight on flame or in a pan with oil, depending on your stove top.
Serve tacos open face with side of birria sauce, some tortilla chips, and a margarita!
