Peel garlic cloves and place in slow cooker.
Chop potatoes into 1-2" pieces and add to slow cooker.
Cover and cook on low for 6-8 hours or high for 3-4 hours.
Drain potatoes and reserve liquid.
Put potatoes back in slow cooker and mash.
Heat cream and butter until hot and butter is nearly melted.
Add cream mixture, parmesan, salt and enough of the reserved liquid to reach desired consistency.
Keep on warm until ready to serve.