Rich chicken tortilla soup, made from slow-simmered chicken thighs, joins quintessential toppingsavocado, red onion, sour cream, cilantro, cheese, tortillas, limes and hot saucein this simple, sustaining slow-cooker meal. The broth gets both depth and brightness from chili powder, smoky chipotles, fire-roasted tomatoes, cumin, and a couple of secret ingredients: unsweetened cocoa powder and apple cider vinegar.