Toast the dried guajillo and ancho chilies in a dry skillet over medium heat for about 2-3 minutes.

Remove the chilies from the skillet and place them in a blender with chopped onion, minced garlic, cumin, oregano, black pepper, and 1 cup of chicken broth, then blend until smooth.

In a large pot or Dutch oven, add the remaining chicken broth and the blended sauce. Bring to a simmer and add the chicken thighs. Cook for about 1.5 hours until the chicken is tender.

Remove the cooked chicken from the pot and shred it using two forks.

Use a strainer to separate the solids from the broth.

Warm the corn tortillas in a skillet over medium heat for about 30 seconds on each side.

Fill each tortilla with a generous amount of shredded chicken and top with chopped onions and fresh cilantro.

Serve the tacos with a small bowl of the strained broth for dipping.