In a pinch this dish can be made with boneless chicken breast, but for the most flavorful broth bone-in breasts with their skin still on is the best choice.
The heat in this dish is up to you— 2 chipotle peppers makes for a mild dish with a hint of smokiness. 3 to 4 is medium. The best thing to do is to taste the tomato sauce once it's been blended with the peppers and adjust to your liking. Keep in mind that the heat will get diluted with the chicken and onions.
2 chicken breasts
3 cloves of garlic
2 Tablespoons olive oil
4 garlic cloves, microplane or press to a pulp
(1) 15 ounce can of chopped tomatoes
1 can chipotle peppers in adobo
1 cup of polenta
5 cups chicken broth
1 teaspoon salt
2 Tablespoons butter
1 Tablespoon sour cream, plus more for serving— optional
Cut off the tough green leaves off the leek, slice it in half, and clean it by flipping the layers under running water. Add it to a medium sized pot with a lid. Peel and halve the onion and add it to the pot. Peel and add the garlic. Add 6 cups of water, one teaspoon of salt and bring to a boil. Once boiling add the chicken and bring to a simmer for 10 minutes then cover the pot and let the chicken continue to cook in the hot water for 15 minutes.
Blend the can of tomatoes with the peppers then set aside.
Slice 2 onions and cook them gently over medium heat in a medium pot or dutch oven with 2 Tablespoons of olive oil. Stir them often but not constantly— you want to get them translucent and wilted. They are ready when they take on a bit of color—about 20 minutes.
Once the onions are cooked add the tomato chipotle sauce to the pot. Taste and adjust the salt.
Preheat your oven to 350.
Once the chicken is cooked remove it from the hot liquid using tongs. Place the chicken on a plate. It's important to shred the chicken as soon as it is out of the hot water. The best way to do this is to tear it apart using two forks.
Add the shredded chicken to the onions and stir.
In an oven safe baking dish mix 1 cup of polenta with 5 cups of the broth and 1 teaspoon of salt cover the dish with a lid or foil and bake for 40 minutes.
Remove from the oven. If you used foil, carefully peel it back. There may be hot steam .
Stir the polenta, then taste it. Is it cooked enough? Does it need more time? It will most likely need another 20 minutes. Cover it up again and continue to cook it.
After the 20 minutes, check again for tenderness. It should be done. Stir in the butter, and the Tablespoon of sour cream if using, and let the polenta cool a bit. It will firm up.
Re-heat the tinga, and serve it with the polenta. Add a dollop of sour cream if you want.
Any left over polenta can be stored in the refrigerator. It will get very firm and can be sliced and pan fried the next day.