Slow Cooker Birria de Res

Name: Slow Cooker Birria de Res
Prep time: 15 min
Cook time: 5 h
Total time: 5 h 15 min
Cuisine: Mexican
Ingredients: 2 tablespoons vegetable oil; 1 teaspoon salt; 1/4 teaspoon pepper; 3 pounds chuck roast (or another fatty pot-roast cut of beef); 1 onion (quartered); 2 stalks celery (cut into 4); 6 cloves garlic (smashed); 2 cups beef broth (low or no sodium added); 1 tablespoon dried cumin; 1 tablespoon Mexican oregano; 1 dried chipotle chili; 3 dried guajillo chilis; 2 dried pasilla chilis; 3 dried ancho chilis; 5 chiles de arbol (more if you like it spicy, less if you like it mild); 1/2 cup diced sweet onion (optional garnis); 1/4 cup chopped cilantro (optional garnish); 1 lime (optional garnish)