Methods

1. Place the potatoes and 2 tablespoons salt in a large pot, and add cold water so the potatoes are covered by a couple inches. Cover with a lid, place over medium-high heat, and bring to a rolling boil. Reduce the heat to medium and gently boil until the potatoes are cooked through and can easily be pierced with a paring knife, 22 to 30 minutes, depending on the size of your potatoes.
2. Meanwhile, the milk, heavy whipping cream, butter, garlic, thyme sprigs, if using, 1¼ teaspoons salt, white pepper, and nutmeg in a medium saucepan, cover, place over medium heat, and bring to a gentle boil. Reduce the heat to low and simmer, covered, for 30 minutes (or, the time it takes the potatoes to cook).
3. Drain the potatoes and return back to the pot they cooked in for a few minutes (this will make sure any excess water steams off). Remove the thyme sprigs from the warm, infused milk mixture. Rice the potatoes into the saucepan with the warm milk and butter, and gently fold in. Alternatively, add the potatoes to the cream, and use a potato masher to mash together.
4. Taste and adjust salt, white pepper, and nutmeg. Transfer to a warm serving dish and serve with an extra pad of butter on top, if desired.