Put the potatoes, broth, and milk into the slow cooker. Sprinkle the garlic and 4 tablespoons of the butter on top. Sprinkle with salt & pepper.
Cook for 3-4 hours on high or 6-8 hours on low, or until the potatoes are super soft. Use a potato masher or hand mixer to pureé the potatoes to your desired texture. (I liked these really creamy!)
Stir in the sour cream and more salt & pepper to taste.
Top with the remaining butter in pats.
Keep warm until ready to serve.
If you are going to be waiting awhile to serve these, I suggest topping the crock pot with a clean towel and then placing the lid on top. This will absorb the steam and keep the potatoes from getting gummy.
Recipe adapted from All Recipes