In a Dutch oven or large stockpot, add potatoes and 2 tablespoons salt. Add cold water to cover potatoes by 1 inch.
Over medium-high heat, bring to boil and partially cover pot. Cook until potatoes are tender and a fork can be easily slipped into the center, stirring once or twice, about 10 to 15 minutes. Drain well, tossing in colander to remove excess water.
Wipe pot dry. Return potatoes to pot and mash to a uniform consistency. Using a rubber spatula, fold in melted butter until just incorporated.
Slowly stir in 1 1/2 cups hot milk. Add more milk, 1 tablespoon at a time, to adjust the consistency as desired. Season to taste with salt and pepper.
Potatoes: For the fluffiest, smoothest, and most flavorful mashed potatoes, choose high-starch potatoes like Russet, Idaho, or Yukon gold potatoes. Waxy potatoes (such as new, red, or white varieties) require more mashing to become creamy which could result in gluey, pasty spuds.
Butter before milk:Always add the butter first so the butter fat coats the potato starch molecules. Then, add the hot milk to make them creamy. If you mix up the order, you could end up with gluey spuds. (Thanks Cook's Illustrated for this tip!)
Yield: This recipes makes about 12 cups mashed potatoes, enough for 12 (1-cup) servings.
Storage: Store leftovers covered in the refrigerator for up to 4 days.
Make ahead: Peel and cube the raw potatoes up to 24 hours in advance. Cover with water and chill in the refrigerator.
Freezer: Mashed potatoes wind up watery and unappetizing after thawing from frozen (unless the recipe is created for that purpose such as our freezer-defying Make Ahead Mashed Potatoes recipe which uses cream cheese and egg whites for a little more staying power).