Peel potatoes and quarter lengthwise; cut crosswise ½ inch thick. In a 5-quart saucepan, combine potatoes and garlic cloves; cover with water (about 8 cups) by 1 inch.
Add 1 tablespoon salt. Bring to a boil; reduce heat, and simmer until potatoes are easily pierced with the tip of a paring knife, 25 to 30 minutes.
Drain; return garlic and potatoes to pan. Stir over medium-high heat until dry, 1 to 2 minutes.
Remove from heat. In a small saucepan, bring milk to a boil; pour over potatoes.
Add butter and 1 teaspoon of salt. Mash by whatever method you prefer until smooth and creamy.
