Place peeled potatoes, garlic (if using), chicken broth and water in the slow cooker. Cover and cook on high for 2-4 hours (depending on how fast your slow cooker cooks). You want the potatoes to be very tender (just about falling apart).

Allow to sit, uncovered for 2 minutes, then add butter, buttermilk, ½ cup milk and 1 teaspoon salt. Mash well with a potato masher. Add more milk as needed to make a nice creamy, but scoop-able consistency. Taste and add more salt, if need.

Serve immediately or hold in slow cooker till ready to serve. Potatoes will keep well for 2-3 hours on warm setting of slow cooker. Just before serving, stir and add more milk if needed for desired consistency

To make ahead, follow directions 1-3 above. Allow to cool then transfer to a storage container and refrigerate for 1-2 days. To rewarm, transfer potatoes to slow cooker at least one hour before serving. Add ½ cup milk and and adjust heat to low. Allow to warm for one hour or more. Stir well and add more milk if needed to reach desired consistency.