Brush chicken thighs with olive oil and sprinkle with salt, and pepper on both sides. In a dutch oven, fry the chicken thighs for 3 minutes on each side until golden brown. Remove and set aside.
Add the diced onion and garlic for 5 minutes on low heat until fragrant. Next, add tomato sauce, chopped tomatoes, all your spices, salt, bay leaf, pour in broth, chicken thighs and add guajillo peppers to the pot. Mix everything thoroughly.
Cover the pot with a lid and cook on medium heat for an hour (or until meat shreds easily with forks). After an hour, remove the thighs, or beef and set aside, discard the bay leaf from the broth, and tear off the tails from the peppers.
Place the remaining ingredients in a blender and blend until a smooth. If the sauce seems too thick for you, add a little broth or water to bring it to the desired consistency.
Chop your cooked chicken and put into a bowl. Add approximately 4 tablespoons of the sauce into the bowl with the chopped chicken meat, stir. Serve inside tortillas this way if you'd like tacos.
To make birria quesadillas though you would pour the remaining sauce into a wide bottom bowl. Roll the tortilla on both sides in it so it's coated. Put the tortilla in the hot pan.
Add some of the chopped chicken meat on one half of it, sprinkle with lots of cheese on top. Cover with the other half of the tortilla and fry for about 3 minutes until the tortilla becomes crispy around the edges and cheese is melted.
Can add more chopped onion, cilantro, salsa or guacamole inside too before melting if desired.