Step 1Cook chicken in oil in skillet over medium heat until browned, 6 to 8 minutes each side. Cook in batches, if necessary. Remove skin and set chicken aside in Dutch oven.
Step 2Combine milk, 1/2 cup crema, chipotles to taste and salt to taste in heavy saucepan. Bring to boil. Pour into blender and blend until smooth. Pour sauce over chicken and cook over low heat 15 to 20 minutes, turning once. Add remaining 1/2 cup crema and chicken broth, and cook 5 minutes longer, or until cooked through, gently mixing sauce.
Step 3When ready to serve, place chicken on heated platter. With scissors, cut California chiles crosswise into thin rings, discarding seeds. Sprinkle chicken with sesame seeds and decorate with chile rings. Accompany with tortillas.