Chop the garlic, carrots, and onion.
Saute over medium heat in a large pot until the vegetables begin to soften. (About 5 minutes.)
In a large saucepan, heat 1 tablespoon of butter or oil in the bottom over medium-high heat. Add the chicken thighs to the butter and sear on both sides until golden brown.
Once the vegetables have softened, add the chipotle peppers in adobo sauce, and the bay leaves. Stir together and let cook for a few minutes.
When the chicken thighs are finished browning on both sides, add them to the pot with the vegetables and adobo peppers.
Pour in the hot water. The amount needed may vary a bit based on your pot size.
Add the chicken bouillon and the rest of the seasonings. Gently stir.
Cook on medium heat, and bring to a boil. Reduce the heat and cook for about 30 minutes.
Remove the chicken from the pot and set aside.
Strain the vegetables from the broth that has been created. Place the chicken back in the pot along with the strained broth.
Place the vegetables in a blender and blend until smooth. Transfer this mixture back into the pot with the chicken.
Cook over medium-low heat and let simmer slowly for 3 hours OR until the meat is tender and easy to shred.
Remove from the heat and use a fork to shred the chicken thighs while still in the pot. Strain the shredded chicken from the sauce. Shred any still large chicken pieces as well as remove the bones and fatty pieces from the chicken.
Prepare a frying pan and the ingredients nearby needed for the tacos. Keep the sauce and shredded chicken separate, the corn tortillas nearby, as well as the extra chopped onions, chopped cilantro, and mozzarella cheese.
Heat the pan to medium-high heat with a bit of oil in the bottom. Dip a corn tortilla into the birria sauce, coating both sides. Place it in the hot pan.
On half of the taco, fill it with the shredded chicken. On the other side fill it with mozzarella cheese. Place a few onions inside the tacos as well.
Use a spatula to flip half the taco over and close. Press the taco down to get a nice sear as well as help the cheese melt into the other side of the taco and stick together. After about a minute or when the taco shell is nicely seared on both sides, remove it from the pan.
Repeat to make the rest of the birria tacos.
Sprinkle the rest of the chopped onions on top and cilantro.
For the side of birria sauce to dip in, use the extra sauce left from the pot and add some chopped onions and cilantro to it.