Place the potatoes, diced onion, diced celery, and chicken broth into the slow cooker. Set it on low and allow it to cook for 5 to 6 hours, or alternatively, use the high setting and cook for 3 to 4 hours until the potatoes become soft.
Once the potatoes are tender, lightly mash them directly in the slow cooker. Then add the flour, ranch seasoning, 2 cups of shredded cheddar cheese, sour cream, salt, pepper, and half and half. Stir everything thoroughly to combine.
Cover the slow cooker again and let the soup cook for another 30 minutes to allow it to thicken and for the flavors to meld.
If you'd like a chunkier texture, serve the soup as is with lightly mashed potatoes. For a smoother consistency, blend the soup gently with an immersion blender until creamy.
To finish, ladle the soup into bowls and garnish with the reserved crumbled bacon, diced green onions, and the remaining shredded cheese before serving.
