Step 1 Arrange a rack in lower third of oven; preheat oven to 425°. Scrub 2 lb. russet potatoes and 2 lb. Yukon Gold potatoes and prick all over with a fork. Place on a foil-lined rimmed baking sheet. Step 2 Halve head of garlic crosswise (as if you're cutting through the equator) and place on a piece of foil.