Line the bottom of a slow cooker with the sliced onion and broth, place the chicken over the onion and cook on high for 2.5 hours.
Transfer the chicken to a plate and shred with two forks. Remove the onion and drain the broth from the slow cooker. Turn it on low and set the timer for 30 minutes. Add the shredded chicken, cream cheese, ranch dressing, hot sauce, cheddar cheese, and mozzarella cheese. Give it a quick stir and allow the mixture to cook.
Mix everything together until fully combined – I like to do a quick taste test here, too. Add more hot sauce if you like it spicy or more ranch if you need to cool it down. Let it all cook for 30 minutes, until the cheese has melted.
If you've tried this recipe, come back and let us know how it was!