Heat oil in a medium Dutch oven over medium heat. Add chicken and cook, turning frequently, until golden brown, about 10 minutes; transfer to a plate. Add onion and cook, stirring frequently until lightly browned, about 8 minutes. Sir in garlic, cumin, salt and cayenne. Cook, stirring constantly, until fragrant, about 30-60 seconds.
Add broth to Dutch oven. Cook, stirring constantly, scraping browned bits from the bottom of the pot, about 3 minutes. Stir in the salsa. Nestle chicken in the onion mixture. Increase heat to medium-high and bring to boil. Reduce heat and simmer, covered, stirring occasionally, until chicken is cooked through, about 25 minutes.
Transfer chicken to a work surface. When cool enough to handle, shred chicken with two forks. Stir chicken, cilantro and sour cream into chili mixture.
Recipe by In Good Taste at http://ingoodtaste.kitchen/chicken-tomatillo-chili/