Remove the stem from a dried chili pepper and soak it in boiling water to rehydrate.
Combine sauce ingredients in a food processor or blender, mixing into a paste. This is the base flavoring for your slow cooked beef cheek tacos.
Pour in beef stock and lime juice, then blend to combine into a sauce.
Arrange the beef cheeks snugly in a baking dish. Pour the sauce over and mix well. Bake uncovered until tender.
Once the slow cooked beef cheeks are tender and the sauce is very thick, remove from the oven. Use two forks to shred the meat.
Serve the shredded meat in soft tortillas with avocado, lime, cilantro, crunchy veggies and spicy chili sauce. I know you'll make these slow cooked beef cheek tacos again and again!