1. Drop the potatoes into a large pot of boiling salted water. When the water returns to a boil, reduce the heat to medium and cook until the potatoes are tender when tested with a fork, about 20 minutes.
2. Meanwhile, in a small skillet, heat the oil over medium low. Add the garlic and sauté, stirring frequently, until soft and browned all over. Set aside.
3. Drain the potatoes thoroughly. Add the garlic, butter, and hot milk and blend with a potato masher until almost smooth. Season with salt and pepper to taste.
Note: The potatoes can be prepared 1 day ahead, covered, and refrigerated. To reheat, place the potatoes in a saucepan over medium heat. Stir in 1/2 cup milk and cook, stirring frequently, until heated through.