- 1 large head of garlic
- 2 tablespoons extra-virgin olive oil
- 3 medium onions, halved lengthwise, each half cut crosswise into 1/4-inch-thick slices
- 2 tablespoons fresh thyme, divided
- 1/2 pound thick-cut bacon, sliced crosswise into 1/4-inch strips
- 1 cup whipping cream
- 1 1/2 pounds Yukon Gold potatoes
- 1 teaspoon coarse kosher salt, divided
- Preheat oven to 400°F. Cut off top 1/2 inch from head of garlic. Wrap garlic in foil and roast until soft, about 45 minutes. Cool. Squeeze garlic cloves into small bowl; mash with fork. Cover and reserve.
- Heat oil in heavy large skillet over medium-high heat. Add half of onions and 1 tablespoon thyme and cook until slightly softened, stirring frequently, about 6 minutes. Add remaining onions and sauté until very soft, about 15 minutes. Reduce heat to medium-low and cook until deep golden brown, stirring frequently, about 40 minutes longer. Set aside.
- Sauté bacon in heavy medium saucepan over medium heat until bacon is beginning to crisp around edges, about 4 minutes. Pour off drippings from pan. Add cream, 1 tablespoon roasted garlic, and 2 teaspoons thyme; simmer until slightly thickened, about 4 minutes. Cool.
- Preheat oven to 400°F. Peel and thinly slice potatoes with mandoline or knife. Spoon 1/2 cup cream mixture over bottom of 8x8x2-inch metal or ceramic baking dish. Arrange 1/3 of potato slices over cream, overlapping as necessary. Sprinkle with pepper and 1/3 teaspoon coarse salt. Spread half of caramelized onions over potatoes. Spoon half of remaining cream mixture over onions. Cover with half of remaining potatoes. Sprinkle with pepper and 1/3 teaspoon salt. Spread remaining onions over potatoes. Spoon all but 2 tablespoons cream mixture over onions. Cover with remaining potato slices. Sprinkle with black pepper and remaining 1/3 teaspoon salt. Drizzle with remaining cream mixture. Sprinkle with remaining 1 teaspoon thyme. Cover tightly with plastic wrap, then foil.
- Bake until potatoes are tender when pierced with knife (pierce knife through foil), about 45 minutes. Carefully remove foil and plastic wrap (steam will be released). (Can be prepared 2 hours ahead. Let stand at room temperature.) Increase oven temperature to 500°F. Bake until top is golden brown, about 10 minutes longer (or about 15 minutes if at room temperature). Let stand 10 minutes. Serve.