In a saucepan or cast iron skillet, preheat the pan over medium heat.
Add the oil and swirl to coat the pan.
Add the onion and cook until softened, 5 minutes.
Add the garlic and cook 30 seconds longer.
Add a splash of the chicken broth and deglaze the pan if needed.
Add the in the remaining chicken broth, crushed tomatoes, chipotle peppers and adobo sauce and stir to combine.
Add the chicken and season with salt and pepper.
Bring to a boil.
Reduce heat, cover and allow the chicken to simmer in the sauce 30 minutes.
Remove from heat and allow to cool 10 minutes.
Remove the chicken from the sauce.
Using an imersion blender, blend the sauce until smooth in the pan or in a large bowl. Alternatively, working in batches, blend in a food processor or blender.
Reserve ½ cup of the sauce and set aside.
Shred the chicken and return it to the remaining sauce, and toss to coat.
Season with salt and pepper to taste.