Add butter to a small saucepan. Heat over medium/low heat until the butter starts to crackle. Once the butter quiets down and the foam clears, stir the butter occasionally until it starts to turn a warm brown color and begins to smell nutty. Once you can see the little brown bits, shut the flame, and take the pan off the heat right away. Transfer the brown butter to a small bowl to cool slightly. To save time and space, this step can be done the day/night before. The butter will melt when it cooks along with the potatoes in the slow cooker.

Peel and roughly chop the potatoes into large chunks. Add the brown butter, garlic, salt, pepper, stock, and milk to the slow cooker. Stir to combine. Add in the potatoes and make sure the potatoes are mostly covered with the liquid.

Cover the potatoes and set the cooker to high and cook for three hours. After three hours, roughly mash the potatoes with a potato masher or, for a creamier texture, puree using an immersion blender.

Keep the slow cooker on warm until ready to serve.