3 pounds Yukon Gold potatoes
1 head garlic (3 inches wide)
3 1/2 tablespoons olive oil, divided
1 1/2 cups whole milk
4 T unsalted butter
1/2 teaspoon white pepper
Preheat oven to 425°. Wrap each potato in foil, then prick potatoes through foil several times with a fork. Cut off and discard 1/2 inch from top of garlic head, exposing cloves. Put garlic on a double layer of foil, then drizzle with 1 tablespoon oil and sprinkle with 1/4 teaspoon salt. Twist foil tightly to enclose. Roast potatoes and garlic on rack in upper third of oven until tender, 1 to 1 1/4 hours.
Unwrap garlic and cool to warm, then squeeze cloves into a large bowl and mash well with a fork. Heat milk, butter, white pepper, and 1 1/4 teaspoons salt in a small saucepan over medium-low heat until butter is melted. While milk mixture heats, unwrap baked potatoes and force through ricer into bowl with garlic. Pour in hot milk mixture and gently stir with a large heatproof rubber spatula until combined.
Note: Because of modifications to the original recipe, we ended up with too much liquid. I've adjusted the amounts to what should work, but add a little at a time, just in case.