In a large pot, combine the potatoes and garlic with enough salted water to cover by 2 inches. Bring to a boil over high heat. Lower to a gentle boil and cook until the potatoes are tender, about 30 minutes.
Meanwhile, in a small saucepan, bring the cream to a simmer over low heat. Remove from the heat and add the butter to melt.
Drain the potatoes and garlic and return to the pot. Shake the pan over medium heat for 1 minute to dry the potatoes. Put the potatoes and garlic through a food mill or ricer and add the cream mixture along with 1 tsp. salt, stirring until smooth. Spoon into a serving bowl.