Next, take your garlic and chop each piece roughly into halves or thirds, and throw these into the pot with the potatoes.
Turn your heat to high. When the water comes to a boil, drop the heat to medium to medium-high so that you don't have water boiling over the sides. After about 15 minutes, start checking the doneness of the potatoes by poking them with a sharp knife - if it goes in and comes out of the pieces easily, they're done. You may have to keep them boiling for another 5 or so minutes.
Not ready to serve just yet? That's fine - kill the heat, and the potatoes will be fine for another 15 minutes or so (after that, they start to take on too much water and become soggy).
Getting ready to serve? Great - strain the potatoes and garlic, and put them back in the pot with your butter, salt and pepper, and milk. Either with a masher or a fork, loosely mash the potatoes (I like them a little lumpy).
If you're still not quite ready to serve, or you need another cocktail before laying out your plates, you can put a lid on your pot and the potatoes will stay good and hot for another 5 to 10 minutes.