Put 900g of boneless, skinless chicken thighs, ¼ large onion, 2 garlic cloves, 1 bay leaf, and 1 teaspoon of kosher salt in a pot. Cover with water by 1in / 2.5cm.
Bring to a boil, cover and simmer for 15-20 minutes, until the chicken reaches 165°F / 74°C. Reserve the cooking broth. Rest the chicken for 5 minutes, then shred.
Meanwhile, halve 1 large white onion. Place it with 4 large Roma tomatoes on an oiled baking sheet. Broil on high for 10 minutes, turning halfway, until charred in places.
Blend the roasted vegetables with 2 tablespoons of chipotle peppers in adobo sauce, 2 more garlic cloves, 1 teaspoon of dried Mexican oregano, 1 teaspoon of kosher salt for the sauce, 1 teaspoon of ground cumin, and ½ cup of reserved chicken cooking broth.
Heat 1 tablespoon of olive oil over medium-high heat. Add the sauce, cover and simmer for 10 minutes, stirring occasionally.
Stir in the shredded chicken and simmer for 10 minutes. Add more reserved broth if needed.
