1. Combine potatoes, 4 tablespoons melted butter, 1 teaspoon salt, and 1/2 teaspoon pepper in a large bowl and toss to coat; set aside. Place garlic and rosemary in a piece of cheesecloth; gather corners and tie into a bundle with kitchen twine.
2. Add broth, 1 cup milk, and herb bundle to a large slow cooker. Add potatoes, spreading them out in an even layer to avoid washing off butter (this will help minimize browning). Drape a clean kitchen towel over slow cooker, then top with lid. Cook on high until potatoes are very tender, about 4 hours.
3. Remove garlic-herb bundle and set aside. Add remaining 1 cup milk and 4 tablespoons melted butter. Using an electric mixer or potato masher, mash potatoes until mostly smooth. When garlic is cool enough to handle, squeeze softened cloves out of skins into a small bowl and mash with a fork. Season mashed potatoes with salt, pepper, and mashed garlic to taste.
4. Eat immediately or cover and keep slow cooker on warm setting for up to 4 hours. Stir in additional warmed milk to loosen before serving if desired.
Source: Hannaford fresh Magazine, December 2018