Bring a large pot that's about half full of water to a boil. Peel and cut the potatoes into 1-inch pieces.
While the water is coming to a boil, add the potatoes, the garlic clove, and about 1 tsp. salt to the water and then simmer for 10 - 15 minutes until the potatoes are fork tender.
Drain the potatoes and garlic and return them to the pot over medium heat, shaking until any remaining water dries.
Transfer the potatoes and garlic to a large mixing bowl.
Add the butter or margarine, milk (or buttermilk, if you have it), thyme, and remaining salt.
Beat with an electric mixer on medium speed until they are just smooth—don’t over-mix (or you can mash them, if you prefer).
Serve immediately or transfer to an oven-safe serving bowl and keep warm in a 300-degree oven until you are ready to serve.